For single seasons, From 1901 to 2008, (requiring W≥21 and L≤6), sorted by smallest ERAp

  Cnt Player            **ERA **  W  L Year Age Tm  Lg  G  GS CG SHO GF  W-L% SV   IP   H   R   ER  BB  SO   ERA  HR  BF   AB  2B 3B IBB HBP  SH  SF GDP  SB CS Pk BK WP   BA   OBP   SLG   OPS  OPS   Pit  Str
 ----+-----------------+--------+--+--+----+---+---+--+---+--+--+---+--+-----+--+-----+---+---+---+---+---+------+--+----+----+--+--+---+---+---+---+---+---+--+--+--+--+-----+-----+-----+-----+----+----+---- 
    1 Jack Morris          102   21  6 1992  37 TOR AL  34 34  6   1  0  .778  0 240.2 222 114 108  80 132   4.04 18 1005  902 41  3   2  10   4   7  15  22 16  0  2  9  .246  .312  .358  .670   84           
    2 Catfish Hunter       107   21  5 1973  27 OAK AL  36 36 11   3  0  .808  0 256.1 222 105  95  69 124   3.34 39 1040  958 39  4   1   1   3   9   8   5 18  3  0  2  .232  .282  .403  .685   95           
    3 Dave Ferriss         113   25  6 1946  24 BOS AL  40 35 26   6  4  .806  3 274   274 109  99  71 106   3.25 14 1141                  3                        0  1                            0           
    4 Alvin Crowder        114   21  5 1928  29 SLB AL  41 31 19   1  6  .808  2 244   238 113 100  91  99   3.69 11 1069                  1                        0  1                            0           
    5 Dave McNally         116   21  5 1971  28 BAL AL  30 30 11   1  0  .808  0 224.1 188  75  72  58  91   2.89 24  899  822 36  3   2   5  10   4  24   1  4  4  0  5  .229  .282  .367  .649   90           
    6 Whitey Ford          117   25  4 1961  32 NYY AL  39 39 11   3  0  .862  0 283   242 108 101  92 209   3.21 23 1159 1056 39  8   3   1   7   3  28   0  3  4  0  8  .229  .291  .347  .638   80           
    7 Bill Donovan         118   25  4 1907  30 DET AL  32 28 27   3  4  .862  1 271   222  96  66  82 123   2.19  3 1103                  8                        0  2                            0           
    8 Gaylord Perry        121   21  6 1978  39 SDP NL  37 37  5   2  0  .778  0 260.2 241  96  79  66 154   2.73  9 1055  970 46  7   8   2   8   9  24  18 16  2  3  4  .248  .295  .338  .633   90           
    9 Ron Guidry           123   22  6 1985  34 NYY AL  34 33 11   2  0  .786  0 259   243 104  94  42 143   3.27 28 1033  980 47  5   3   0   3   8  30   7 10  0  1  3  .248  .277  .392  .669   82           
   10 Bob Welch            126   27  6 1990  33 OAK AL  35 35  2   2  0  .818  0 238   214  90  78  77 127   2.95 26  979  886 42  6   4   5   6   5  25  10  7  0  2  2  .242  .304  .391  .695   96           
   11 Tom Glavine          127   22  6 1993  27 ATL NL  36 36  4   2  0  .786  0 239.1 236  91  85  90 120   3.20 16 1014  910 50  4   7   2  10   2  25   9  5  1  0  4  .259  .327  .376  .703   92           
   12 Jack Chesbro         127   28  6 1902  28 PIT NL  35 33 31   8  2  .824  1 286.1 242  81  69  62 136   2.17  1 1163                 21                        1  3                            0           
   13 Larry Jansen         129   21  5 1947  26 NYG NL  42 30 20   1  5  .808  1 248   241 102  87  57 104   3.16 23  985                  1                        1  2                            0           
   14 Preacher Roe         129   22  3 1951  36 BRO NL  34 33 19   2  1  .880  0 257.2 247  91  87  64 113   3.04 30 1031                  0                        0  2                            0           
   15 Ellis Kinder         130   23  6 1949  34 BOS AL  43 30 19   6 10  .793  4 252   251 103  94  99 138   3.36 21 1085                  2                        0  1                            0           
   16 Doug Drabek          131   22  6 1990  27 PIT NL  33 33  9   3  0  .786  0 231.1 190  78  71  56 131   2.76 15  918  846 37  4   2   3  10   3  11  18  9  4  0  6  .225  .274  .331  .605   74           
   17 Sal Maglie           134   23  6 1951  34 NYG NL  42 37 22   3  5  .793  4 298   254 110  97  86 146   2.93 27 1210                  6                        2  4                            0           
   18 Eddie Plank          140   26  6 1912  36 PHA AL  37 30 23   5  6  .813  2 259.2 234  90  64  83 110   2.22  1 1073                  6                        1  5                            0           
   19 Bob Purkey           143   23  5 1962  32 CIN NL  37 37 18   2  0  .821  0 288.1 260 109  90  64 141   2.81 28 1181 1083 32  3   3  14  13   7  18  15  3  1  1  6  .240  .289  .353  .642   74           
   20 Tex Hughson          144   22  6 1942  26 BOS AL  38 30 22   4  5  .786  4 281   258  92  81  75 113   2.59 10 1150                  1                        1  1                            0           
   21 Chief Bender         149   23  5 1910  26 PHA AL  30 28 25   3  2  .821  0 250   182  63  44  47 155   1.58  1  936                 10                        0  7                            0           
   22 Chris Carpenter      149   21  5 2005  30 STL NL  33 33  7   4  0  .808  0 241.2 204  82  76  51 213   2.83 18  953  884 46  3   0   3   7   7  22   1  5  2  0  5  .231  .273  .351  .624   66 3388 2233 
   23 Curt Schilling       150   21  6 2004  37 BOS AL  32 32  3   0  0  .778  0 226.2 206  84  82  35 203   3.26 23  910  861 54  2   0   5   3   6  12   6  1  1  0  3  .239  .271  .387  .658   65 3414 2386 
   24 Tom Seaver           150   21  6 1977  32 TOT NL  33 33 19   7  0  .778  0 261.1 199  78  75  66 196   2.58 19 1031  954 35  8   6   0   5   6  12  22  7  2  1  7  .209  .258  .322  .580   60           
   25 Tiny Bonham          151   21  5 1942  28 NYY AL  28 27 22   6  1  .808  0 226   199  65  57  24  71   2.27 11  872                  1                        0  1                            0           
 ----+-----------------+--------+--+--+----+---+---+--+---+--+--+---+--+-----+--+-----+---+---+---+---+---+------+--+----+----+--+--+---+---+---+---+---+---+--+--+--+--+-----+-----+-----+-----+----+----+---- 
  Cnt Player            **ERA **  W  L Year Age Tm  Lg  G  GS CG SHO GF  W-L% SV   IP   H   R   ER  BB  SO   ERA  HR  BF   AB  2B 3B IBB HBP  SH  SF GDP  SB CS Pk BK WP   BA   OBP   SLG   OPS  OPS   Pit  Str
 ----+-----------------+--------+--+--+----+---+---+--+---+--+--+---+--+-----+--+-----+---+---+---+---+---+------+--+----+----+--+--+---+---+---+---+---+---+--+--+--+--+-----+-----+-----+-----+----+----+---- 
   26 Denny McLain         154   31  6 1968  24 DET AL  41 41 28   6  0  .838  0 336   241  86  73  63 280   1.96 31 1288 1206 38  5   2   6  10   3  19  19  5  1  0  3  .200  .243  .317  .560   72           
   27 Mike Hampton         154   22  4 1999  26 HOU NL  34 34  3   2  0  .846  0 239   206  86  77 101 177   2.90 12  979  854 31  2   2   5  10   9  38   8  6  2  0  9  .241  .322  .324  .646   69           
   28 Curt Schilling       157   22  6 2001  34 ARI NL  35 35  6   1  0  .786  0 256.2 237  86  85  39 293   2.98 37 1021  968 39  1   0   1   8   5  16   4  9  2  0  4  .245  .273  .402  .675   71 3692 2606 
   29 Barry Zito           158   23  5 2002  24 OAK AL  35 35  1   0  0  .821  0 229.1 182  79  70  78 182   2.75 24  939  836 24  3   2   9   9   7  16  10  9  4  1  2  .218  .289  .340  .629   68 3683 2349 
   30 Howie Camnitz        158   25  6 1909  27 PIT NL  41 30 20   6 11  .806  3 283   207  75  51  68 133   1.62  1 1057                  7                        0  2                            0           
   31 Lon Warneke          159   22  6 1932  23 CHC NL  35 32 25   4  1  .786  0 277   247  84  73  64 106   2.37 12 1117                  2                        0  5                            0           
   32 Sandy Koufax         159   25  5 1963  27 LAD NL  40 40 20  11  0  .833  0 311   214  68  65  58 306   1.88 18 1210 1135 28  6   7   3  13   1   9  11  1  0  1  6  .189  .230  .271  .501   54           
   33 Russ Ford            160   26  6 1910  27 NYY AL  36 33 29   8  3  .813  1 299.2 194  69  55  70 209   1.65  4 1141                  8                        1  5                            0           
   34 Johnny Beazley       162   21  6 1942  24 STL NL  43 23 13   3 15  .778  3 215.1 181  67  51  73  91   2.13  4  890                  3                        0  7                            0           
   35 Juan Marichal        167   25  6 1966  28 SFG NL  37 36 25   4  1  .806  0 307.1 228  88  76  36 222   2.23 32 1180 1128 24  2   3   5   8   3  16  20  7  1  0  3  .202  .230  .312  .542   51           
   36 Bobo Newsom          167   21  5 1940  32 DET AL  36 34 20   3  1  .808  0 264   235 110  83 100 164   2.83 19 1101                  3                        2  2                            0           
   37 Carl Hubbell         169   26  6 1936  33 NYG NL  42 34 25   3  6  .813  3 304   265  81  78  57 123   2.31  7 1202                  5                        0  3                            0           
   38 Roger Clemens        169   24  4 1986  23 BOS AL  33 33 10   1  0  .857  0 254   179  77  70  67 238   2.48 21  997  916 34  2   0   4   4   6  14   8 15  1  3 11  .195  .252  .306  .558   50           
   39 Dazzy Vance          174   28  6 1924  33 BRO NL  35 34 30   3  1  .824  0 308.1 238  89  74  77 262   2.16 11 1221                  9                        0  4                            0           
   40 Lefty Gomez          175   26  5 1934  25 NYY AL  38 33 25   6  5  .839  1 281.2 223  86  73  96 158   2.33 12 1142                  0                        0  3                            0           
   41 Joe Wood             178   34  5 1912  22 BOS AL  43 38 35  10  5  .872  1 344   267 104  73  82 258   1.91  2 1362                 12                        0  7                            0           
   42 Bret Saberhagen      180   23  6 1989  25 KCR AL  36 35 12   4  0  .793  0 262.1 209  74  63  43 193   2.16 13 1021  961 45  6   6   2   9   6  13   5  9  3  1  8  .217  .251  .317  .568   59           
   43 Russ Ford            181   21  6 1914  31 BUF FL  35 26 19   5  9  .778  6 247.1 190  63  50  41 123   1.82 11  948                  7                        0  0                            0           
   44 Lefty Grove          185   28  5 1930  30 PHA AL  50 32 22   2 17  .848  9 291   273 101  82  60 209   2.54  8 1191                  5                        0  2                            0           
   45 Randy Johnson        188   21  6 2001  37 ARI NL  35 34  3   2  1  .778  0 249.2 181  74  69  71 372   2.49 19  994  890 33  2   2  18  10   5  17  19 15  4  1  8  .203  .274  .309  .583   50 4052 2627 
   46 Randy Johnson        197   24  5 2002  38 ARI NL  35 35  8   4  0  .828  0 260   197  78  67  71 334   2.32 26 1035  945 42  5   1  13   4   2  19  19 15  3  2  3  .208  .273  .346  .619   59 3962 2605 
   47 Ron Guidry           208   25  3 1978  27 NYY AL  35 35 16   9  0  .893  0 273.2 187  61  53  72 248   1.74 13 1057  969 34  5   1   1  13   2  15   9 14  2  1  7  .193  .249  .279  .528   50           
   48 Roger Clemens        213   21  6 1990  27 BOS AL  31 31  7   4  0  .778  0 228.1 193  59  49  54 209   1.93  7  920  847 35  5   3   7   7   5  11  14 14  2  0  8  .228  .278  .306  .584   60           
   49 Lefty Grove          219   31  4 1931  31 PHA AL  41 30 27   4 10  .886  5 288.2 249  84  66  62 175   2.06 10 1160                  1                        0  2                            0           
   50 Christy Mathewson    222   25  6 1909  28 NYG NL  37 33 26   8  4  .806  2 275.1 192  57  35  36 149   1.14  2 1021                  0                        0  4                            0           
 ----+-----------------+--------+--+--+----+---+---+--+---+--+--+---+--+-----+--+-----+---+---+---+---+---+------+--+----+----+--+--+---+---+---+---+---+---+--+--+--+--+-----+-----+-----+-----+----+----+---- 
  Cnt Player            **ERA **  W  L Year Age Tm  Lg  G  GS CG SHO GF  W-L% SV   IP   H   R   ER  BB  SO   ERA  HR  BF   AB  2B 3B IBB HBP  SH  SF GDP  SB CS Pk BK WP   BA   OBP   SLG   OPS  OPS   Pit  Str
 ----+-----------------+--------+--+--+----+---+---+--+---+--+--+---+--+-----+--+-----+---+---+---+---+---+------+--+----+----+--+--+---+---+---+---+---+---+--+--+--+--+-----+-----+-----+-----+----+----+---- 
   51 Dwight Gooden        228   24  4 1985  20 NYM NL  35 35 16   8  0  .857  0 276.2 198  51  47  69 268   1.53 13 1065  986 23  3   4   2   6   2  21  22 10  5  2  6  .201  .254  .270  .524   52           
   52 Pedro Martinez       243   23  4 1999  27 BOS AL  31 29  5   1  1  .852  0 213.1 160  56  49  37 313   2.07  9  835  780 38  0   1   9   3   6  11  21 10  0  0  6  .205  .248  .288  .536   35           
   53 Mordecai Brown       253   26  6 1906  29 CHC NL  36 32 27   9  4  .813  3 277.1 198  56  32  61 144   1.04  1 1062                  4                        1  2                            0           

Seasons/Careers found: 53.

 Photos from the George Grantham Bain Collection at the Library of Congress.