Max Scherzer Roger Clemens Kerry Wood

On Wednesday night, Max Scherzer accomplished something baseball has not seen for 18 years. The Nationals pitcher struck out 20 batters in a nine-inning game. Scherzer is the third pitcher to do it, and it has happened on four occasions. Two other pitchers recorded 20 strikeouts in extra-inning games.

Here are the MLB's six single-game instances of pitchers striking out 20 hitters:

Max Scherzer (May 11, 2016, 3-2 win vs. Detroit Tigers)

Max Scherzer

Scherzer recorded 20 K's against the Tigers, the team he won an AL Cy Young with in 2013. During his final season in Detroit, 2014, Scherzer turned down a six-year, $144 million extension. The bet on himself turned into a seven-year, $210 million contract with a $50 million signing bonus from the Nationals. He seems to be backing that up with this performance and two no-hitters last season.

Kerry Wood (May 6, 1998, 2-0 win vs. Houston Astros)

Kerry Wood

In his fifth career start, Wood fanned 20 Astros hitters at Wrigley Field. Houston's lineup included the Killer B's of Craig Biggio, Derek Bell and Jeff Bagwell, along with Moises Alou and Brad Ausmus. Wood allowed only one hit to shortstop Ricky Guitierrez. The Texan went on to win the NL Rookie of the Year that season, but after undergoing Tommy John surgery, missed all of 1999. Wood played another 13 MLB seasons, never living up to his initial success. He retired with an 86-75 record, a 3.67 ERA and 1,582 strikeouts.

Roger Clemens (April 29, 1986, 3-1 win vs. Seattle Mariners)

Roger Clemens

Clemens won seven Cy Young Awards, but 1986 may have been his greatest campaign. Clemens went 24-4 with a 2.48 ERA. If it was not for Bill Buckner, the Red Sox would have won the World Series. As for Clemens' 20-strikeout performance, he set the record by giving up only three hits, one being a Gorman Thomas solo home run. Clemens moved to 4-0 with the win. Buckner went 2-for-4 at the dish that game.

Roger Clemens (September 18, 1996, 4-0 vs. Detroit Tigers)

Roger Clemens Pitch

Clemens reached 20 strikeouts a second time, ten years later, in almost completely opposite settings. Rather than early in a successful season, Clemens stumbled into a game at Detroit with a 9-12 record for a Red Sox team about to miss the playoffs. But Clemens took advantage of a horrendous Tigers team that had lost ten straight, allowing only five hits. Clemens left the Red Sox after the season for the Blue Jays.

Tom Cheney (September 12, 1962, 2-1 win vs. Baltimore Orioles, 16 innings)

Tom Cheney

Tom Cheney was not really a strikeout pitcher, and even in his 20-strikeout game for the Senators, the percentages prove that. Cheney went 16 innings and faced 62 batters in his 21-strikeout performance. That is 33.9 percent of the hitters he faced, so the equivalent to a pitcher who strikes out about 9 to 13 hitters in a standard complete game (Scherzer faced 33 hitters Wednesday night). Still, give it up for Cheney, who only started 71 games in his career. He retired with 345 strikeouts in 466.0 innings pitched.

Randy Johnson (May 8, 2001, 4-3 win vs. Cincinnati Reds, 11 innings)

Randy Johnson

The Big Unit really got short-changed. During a Cy Young season for the Diamondbacks that saw him win 21 games and win his lone World Series ring, Johnson struck out 20 Reds. Unfortunately for him, his one run allowed was par with Cincinnati starter Chris Reitsma's one run in eight innings, and the game went into extras. Johnson was relieved after nine innings, but MLB record books still recognize his performance as coming in an extra inning game, despite accomplishing his 20-strikeout task before the tenth. Arizona did win the game, 4-3 in 11 innings.

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-- Follow Jeffrey Eisenband on Twitter @JeffEisenband.