Aaron Boone strode to the mound with a purpose. His starting pitcher had given all he had, but now it was time for a change. The Yankees manager reached out his right hand to ask for the ball, offered a reassuring pat, then sent Luis Severino to the showers. It was time for the bullpen to go to work.

What made this pitching change so fascinating was its timing. Wednesday night's starter Severino had recorded just 12 outs before getting the hook. He'd held the visiting A's scoreless through his first four-plus innings. And he'd allowed just two hits, both of them coming to lead off the fifth -- meaning that just a few minutes earlier, he'd been working on a no-hitter.

Ten years ago, pulling your ace starting pitcher, working on a two-hit shutout in the fifth inning, would have been unthinkable, even in a playoff game. In this case, Severino had thrown just 87 pitches, helping his team build a 2-0 lead. Hell, a decade ago a majority of managers might've left him in to pitch the fifth, for no more complicated reason than to line up their pitcher for the win.

That's not how baseball works in 2018. When Boone popped out of the dugout in the fifth inning of the Yankees' Wild Card Game against Oakland, his mind went to the previous inning, when Severino had worked out of a high-stress, bases-loaded jam. Severino's lack of control that yielded four Oakland walks superseded the two-hit shutout in progress. And the idea of leaving his pitcher in to reach an arbitrary in-game milestone in the hopes of chasing a meaningless stat would be considered misguided, incredibly foolish, and asking for trouble -- if Boone even thought about it at all.

The Yankees went on to beat the A's 7-2, advancing to the League Division Series where they'll take on their arch rivals from Boston. And while thunderous hits by sluggers Aaron Judge, Luke Voit, and Giancarlo Stanton helped carry the Bronx Bombers to victory, the turning point of the game happened the second Boone took his first step onto the field, on the way to pulling Severino.

After pulling his ace, Boone tapped human Sequoia tree Dellin Betances to put out the fifth-inning fire. It wouldn't be easy. Singles by Jonathan Lucroy and Nick Martini had set the stage for the most dangerous part of Oakland's order, with Matt Chapman, Jed Lowrie, and 2018 MLB home-run king Khris Davis due to follow. Moreover, the choice of Betances probably scared a few Yankees fans with long memories. The 6-foot-8 right-hander was just a year removed from an incredibly wild campaign, one that had seen him walk a terrifying 44 batters in 59 2/3 innings, prompting Boone's predecessor Joe Girardi to buy a lifetime supply of Pepto Bismol.

But the Betances of 2018 was a different pitcher than the one we'd seen in 2017. In both cases, he'd affirmed his status as one of the most prolific strikeout artists in major-league history. Only instead of walking the world, Betances had sliced his base-on-balls rate from a vertigo-inducing 16.9 percent last season to a slightly elevated but far more manageable 9.6 percent this year. He'd done so pushing his K rate to an astronomical 42.3 percent, a new career high. Numbers aside, Betances was now doing what baseball old heads valued most in pitchers: He trusted his stuff. Even in the most nerve-wracking situations with no margin for error, Betances believed he could throw any of his pitches any time, and throw any of them for strikes.

So when the power-hitting Chapman walked to the plate with a chance to give the A's the lead in this do-or-die game, Betances decided he didn't want to give in by simply throwing a very hard but potentially straight fastball. Instead, he snapped off a knuckle-curveball, a gorgeous, 86-mph, big-bending yakker that clipped the outside corner by the tiniest of margins. Given the score, the game situation, and Betances' frequent fight to overcome shaky command, that curve will go down as one of the biggest tone-setting pitches of the entire 2018 season.

Two pitches later, Betances fired a nearly identical pitch, inducing a weak flyout to right field. Just like that, he'd turned the inning around, right when the Yankees needed it most.

Betances got away with a mistake to the next batter, throwing a fastball right down the middle that produced nothing more than another harmless flyout. That set the stage for Betances' showdown with the 48-homer planet eater, Davis. Check out the three delicious curveballs that Betances unleashed to punch out Davis and end what would turn out to be Oakland's biggest close-game threat of the night:

All told, 15 of the 25 pitches Betances threw Wednesday were curveballs, with 11 of those 15 going for strikes. When not bending reality with that bender, he dialed up his fastball to 99 mph. This was Betances at his absolute best, right when he really needed it.

Now here comes the really scary part for the Yankees' playoff opponents, starting with the Red Sox: Betances is just one devastating arm in a bullpen that's absolutely full of them. Chad Green was the multi-inning terror who struck out more than six batters for every one he walked. David Robertson was the former closer who thrived alongside Betances in a setup role. Trade deadline acquisition Zach Britton added an additional experienced lefty to a pen stuffed with lights-out righty. And Aroldis Chapman remained the fire-breathing stopper whose top-end fastball topped 103 mph. Yankees relievers led the majors this year in Wins Above Replacement and strikeout rate, proving all season that they could handle heavy volume and heavy hitters alike.

New York's National League equivalent is Milwaukee. Milwaukee. Brewers relievers led the NL in strikeout rate, finished second behind only surprising San Diego in Wins Above Replacement. The Crew's crew improved as the season wore on, too. Corey Knebel went from 2017 All-Star to getting sent to the minors on Aug. 23. But his final month looks like something ripped out of a video game: 14 innings, 30 strikeouts, 3 walks, 5 hits, and a 0.00 ERA. Knebel's end-of-season brilliance solidified arguably the best trio of relievers for any remaining playoff team, with Andrew Miller clone Josh Hader and hard-throwing right-hander Jeremy Jeffress suffocating every opponent in sight. Throw in veteran righty Joakim Soria and you have another ludicrously deep bullpen, armed and ready for October.

If the Yankees and Brewers can get to the sixth inning of any playoff game tied or ahead, bet the farm on them pulling off the W. But even that might be underestimating what both these teams could do with their loaded pens. Thanks to frequent days off throughout the month, the Yankees' Boone and Brewers manager Craig Counsell could push their relief corps even harder. Neither New York nor Milwaukee possesses an elite rotation, making quick hooks even more likely.

Bottom line: Boone coming out in the fifth to get his starter in the middle of a shutout might prove lax compared to how aggressively he and Counsell could run their pens in the coming days and weeks. The game has already changed so much, with fewer and fewer managers pushing their starters deep into games. If we get a Yankees-Brewers World Series, the entire baseball universe might topple over.

Special thanks to Nick Pollack for helping with this piece. Nick will be collaborating on CBS Sports baseball content throughout the postseason. You can find more of Nick's work at his site Pitcher List and at FanGraphs.