Conventional wisdom suggests that a (fill-in-the-blank-superlative) starting rotation is key for a World Series run. After watching the postseason unfold over the last three years, though, I’m not so convinced that’s the only way.

Before we continue, I want to make clear what I’m not saying. I’m not saying that a good starting rotation presents no value, nor am I saying that you can get by with a terrible starting rotation. What I am saying, however, is that there are multiple paths to a title and that one of those paths can include just “good” or even “average” performances from a starting rotation, so long as the bullpen rises to the occasion.

Call me crazy, but after the last three years, if you gave me the option of having an average rotation and a dominant bullpen or the other way around, I’d take the dominant bullpen.

Over those three seasons, all playoff teams have used their bullpen for an average of four out of every nine innings. During the ten seasons prior to that three-year stretch (2004-2013), relievers were used a full-inning less on average. While I’m not totally sure why that was the case, I imagine the growing use of analytics that favors fireballing relievers over starters who are losing steam in the later innings plays a role and, in general, guys are throwing harder and are more effective out of the pen than ever before.

One advantage the bullpen has in the post-season in comparison to the regular season is added off-days. An MLB team averages less than an off-day per week during the regular season. In the playoffs, teams typically get a day off every time the series changes locations. For last year’s 7-game World Series, each team benefitted from two off-days during the series, not to mention nearly a week off for the Indians and two days off for the Cubs prior to the series starting. This allows teams to pitch its best relievers just about every game. On a given night in the regular season, a team might be forced to use its sixth best reliever to get three critical outs in the eighth inning because some of their better relievers might be unavailable due to recent usage. That almost never happens in the post-season.

A part of the modus operandi of the Royals teams that made back-to-back World Series appearances was a nearly-bulletproof bullpen. Their starting rotation was fine, but they certainly didn’t have star power.

The 2015 Royals won the World Series despite producing a post-season rotation ERA of 4.97, which is not only not a dominant number, but just flat out isn’t a very good number. How did they do it? Their bullpen posted a 2.51 ERA and blew just one save, a game they’d ultimately win anyway. In the World Series, which they won in 5 games over the Mets, their bullpen posted 1.90 era.

Last year, the rotation-ravaged Indians cruised to an American League pennant and then lost to the dominant Cubs in extra innings of game 7 in the World Series. They did all that despite the fact that several proclaimed their chances obsolete when it became clear that two of their three best starters–Carlos Carrasco and Danny Salazar–would be unavailable to make starts for them during the playoffs due to injury.

In fairness to the band-aid rotation the Indians wheeled out there, they produced a 3.12 ERA, but that’s because Tribe manager Terry Francona leaned heavily on a bullpen that ended up throwing just five fewer innings than its rotation. Essentially, Francona’s rotation, a unit that averaged fewer than 5 innings/start in the playoffs, worked until the first sign of danger before giving way to the bullpen.

Of the last 6 teams to make it to a World Series, four of them, including the 2014 World Series winning Giants, used their bullpen for at least 4.1 innings per game, which is basically half of the game!

The 2015 Rangers ultimately losing to the Blue Jays in a heartbreaking deciding contest in the ALDS, however, their exit was in spite of a great bullpen showing. In five games, the Rangers’ pen posted a 1.52 ERA. Both Shawn Tolleson (0 runs in 3 innings) and Jake Diekman (1 run in 6 innings) were critical to the team’s success.

Meanwhile, whereas some of these super bullpens have flourished, super rotations haven’t had the same luck of late.

Neither the 2015 Dodgers with Kershaw and Greinke nor the 2014 Nationals, who led MLB in rotation ERA with guys like Strasburg, Fister, and Zimmermann, won a single playoff series.

Of the 24 World Series competitors since 2005, just two completed their post-season journey with a bullpen ERA that exceeded 4.00. Incidentally, those two teams were the 2010 and 2011 Rangers.

Again, I’m not saying it is bad to have a great rotation, but many people talk about a “playoff rotation” like its the determining factor in postseason success, but recent data suggests we should spend equal time talking about a team’s “playoff bullpen.”