Chances are 38-year-old middle relievers don’t usually become stars overnight, but due to injuries in the Boston Red Sox bullpen, Koji Uehara had the opportunity to become one this summer. After months of dominance, Boston and its new closer head to October as a candidate to reach the World Series. 

In the aftermath of Mariano Rivera’s farewell, baseball fans in New York, Boston and around the country can agree on the importance of having a relief pitcher capable of getting the biggest outs in October. In order for the Red Sox to thrive in the postseason, they’ll need the insanely dominant Uehara to maintain his amazing season under the pressure of the brightest lights in the sport.

Before finding a way to dissect if Uehara is ready for the challenge, let’s take a minute to reminisce about the season he just completed.

As the table below shows, the Red Sox closer has posted the third-best single-season SO/BB ratio in the history of relief pitchers with a minimum of 70 innings. When including ERA+ into the equation, it’s reasonable to make a case that the top three seasons in the history of relief pitching belong to Dennis Eckersley, Koji Uehara and Mariano Rivera.

That, folks, is amazing company.

Of course, as we’ve seen over the last two decades with closers like Mark Wohlers, Billy Wagner, Brad Lidge and Joe Nathan, regular-season success doesn’t always transition to postseason dominance.

With Uehara, however, expect his full body of work in America to translate into and through October. In other words, after examining body of work for the Japanese reliever, it’s clear that he’s not a one-hit wonder. The Red Sox have a dominant reliever set to give them a big weapon against the American League postseason field.

While all of Uehara’s numbers (72.1 IP, 99 SO, 9 BB, 1.12 ERA, 21 SV) are impressive, his ability to bear down when runners reach base gives an indication that he will be prepared to escape pressure-packed jams in the postseason.

For the season, Boston’s closer limited batters to a .149 batting average with runners in scoring position. That number dropped to .132 with any runners on base. The path to a 1.12 ERA was filled with stranding runners on the basepath.

Furthermore, Uehara excels, both in 2013 and for the full body of his career since 2009, at dominating hitters in high-leverage situations. While the term can be self-explanatory, we’ll let the folks at Baseball-Reference define what high leverage means in the context of each game.

As stated on B-R’s website, high-leverage is defined:

Within a game, there are plays that are more pivotal than others. We attempt to quantify these plays with a stat called leverage index (LI). LI looks at the possible changes in win probability in a give situation and situations where dramatic swings in win probability are possible (runner on second late in a tie game) have higher LI’s than situations where there can be no large change in win probability (late innings of a 12-run blowout).

Or, to put it simply, when the game is on the line and the outcome undecided, Uehara is at his best. In 2013, opposing batters posted a .124/.149/.206 slash line against the Red Sox reliever in those situations. For the entirety of his Major League Baseball career, the opposition has hit .193/.215/.320 in high-leverage spots against him. During those moments, his strikeout-to-walk ratio is an insane 11.56.

To put those numbers into perspective, when a game is hanging in the balance, Uehara has reduced the opposition to hitting like pitchers and had pinpoint control better than Curt Schilling in his prime.

Predicting the outcome of random October moments before they arrive is presumptuous, but if Red Sox fans are looking to have confidence in the biggest moments of an ALCS game against the Detroit Tigers, the career numbers of 2013’s best reliever don’t lie. 

Time will tell if Uehara steps up to become an October hero, but his entire body of work suggests he’s ready for the challenge of a Miguel Cabrera-Prince Fielder-Victor Martinez challenge in a one-run game next month.

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