A version of this story originally ran on the 10th anniversary in 2022.

There have only been 23 perfect games thrown in MLB history. Today is the anniversary of maybe the most unlikely one of all.

It's Philip Humber's. On April 21, 2012, Humber was perfect for the White Sox, retiring all 27 batters against the Mariners with nine strikeouts to achieve one of baseball's rarest feats.

You would think to be perfect, you have to be great first. And it's true, the list of perfect game pitchers is mostly Hall of Famers, Cy Young Award winners and multi-year All-Stars. But it also has Humber.

• All-time perfect games in MLB history

A top prospect turned 29-year-old journeyman who'd just finally stuck around a big league rotation for a full season, Humber was making his 30th MLB start when he took the mound that Saturday afternoon at Safeco Field. Two hours and 17 minutes later, he'd treated 22,472 fans to the 21st perfect game ever thrown -- and the third by the White Sox, following Mark Buehrle and Charlie Robertson.

Humber's perfect game started innocuously enough: Chone Figgins rolled over a hanging breaking ball, Humber chugged over to cover first for the out. Ordinary. But then he struck out the side in the second. And he struck out Ichiro. And his slider was unhittable. And he kept getting the Mariners out 1-2-3. Suddenly there were two outs in the bottom of the ninth, and Humber had gone 26 up, 26 down.

The 27th out was the craziest. Humber ran the count full to pinch-hitter Brendan Ryan. One pitch for perfection ... and Humber yanked a slider -- so far out of the zone that A.J. Pierzynski couldn't catch it and it trickled off toward the backstop. But wait … did Ryan swing? It was a check swing. Home-plate umpire Brian Runge nearly jumped out of his shoes making the call: yes, Ryan went around. Strike 3.

Ryan was incensed. He turned to argue. If he just ran, he might have been safe. But by the time he turned up the line, Pierzynski had corralled the loose ball and was firing it to first for the final out.

Innocuous start, insane finish. Humber had his perfect game all the same.

But did Humber throw the unlikeliest perfecto in MLB history? Let's run down the list of perfect games and find out.

The 19th-century pitchers: Lee Richmond, John Ward (1880)

Richmond and Ward threw the first two official perfect games, but let's stick to the modern era for now. All bets were off in 1800s baseball. Pitchers weren't even allowed to throw overhand until 1884. Moving on.

The Hall of Famers: Cy Young (1904), Addie Joss (1908), Jim Bunning (1964), Sandy Koufax (1965), Catfish Hunter (1968), Randy Johnson (2004), Roy Halladay (2004)

They're the most likely pitchers to throw a perfect game.

The Cy Young winners: David Cone (1999), Félix Hernández (2012)

Not Hall of Famers (Félix pending), but they were at one time the best pitcher in their league. Next.

The All-Stars: Len Barker (1981), Mike Witt (1984), Tom Browning (1988), Dennis Martinez (1991), Kenny Rogers (1994), David Wells (1998), Mark Buehrle (2009), Matt Cain (2012)

Cain, Buehrle, Boomer, Rogers, Martinez and Witt were all multiple-time All-Star pitchers. You can get a lot unlikelier than that. Browning was an All-Star a few seasons after his perfect game, and he was the NL Rookie of the Year runner-up and a sixth-place Cy Young finisher a few seasons before it. Barker earned his one All-Star nod the same year he threw his perfecto, which was also his second of back-to-back seasons leading his league in strikeouts. They're not the unlikeliest pitchers on the perfect game list either.

That's 19 of 23 … which gives us four candidates for the title of unlikeliest pitcher to throw a perfect game.

The one-hit wonders: Charlie Robertson (1922), Don Larsen (1956 World Series), Dallas Braden (2010), Philip Humber (2012)

These pitchers weren't ever All-Stars, or ERA champions, or Cy Young contenders. But who's the unlikeliest of them all?

Robertson and Braden, at least, threw their perfect games during good years. Robertson, who was pitching his first full big league season for the White Sox, had a 3.64 ERA in 272 innings in 1922; he had a 111 ERA+, meaning he was 11% better than your average pitcher. The A's southpaw Braden had a 3.50 ERA in 192 2/3 innings in 2010; he had a 117 ERA+.

Larsen has a claim to the unlikeliest perfect game, but more for the circumstances than the pitcher. Larsen's World Series gem, the only perfect game in postseason history, is probably the most famous perfecto for that reason. As far as Larsen himself, the Yankees righty had maybe the best season of his career in 1956 even before the perfect game, with a 3.26 ERA in 179 2/3 innings, a personal-best 107 strikeouts and a 119 ERA+.

That leaves Humber. Humber was drafted third overall by the Mets in 2004 out of Rice University, but he never became a Major League star. After being part of the trade package that got the Mets Johan Santana, Humber bounced from the Twins to the Royals to the A's to the White Sox in the offseasons leading up to his perfect game.

Which brings us to 2012. In Humber's perfect game season, he ended up with a 6.44 ERA in 102 innings. His ERA+ was 66 -- way worse than a league-average pitcher. He was in the bullpen by August. He was on waivers by November. By the following September, he'd played his last Major League game.

To look at it another way: Humber's career ERA+ was 81. That's easily the lowest of any pitcher to throw a perfect game.

Lowest career ERA+ by a perfect game pitcher
League average pitcher = 100
Philip Humber: 81
Charlie Robertson: 90
Len Barker: 93
Lee Richmond: 94
Tom Browning: 97
Don Larsen: 99
Dallas Braden: 101

All that makes Humber as unlikely a pitcher as any who has ever thrown a perfect game. But Humber will always have his place in the MLB history books thanks to that day in Seattle, when no pitcher in the world was better than him.