Just a couple of days ago, the Houston Astros were in big trouble. Luis García and José Urquidy — the starting pitchers for Games 2 and 3 of the ALCS — got roughed up in consecutive outings, as the Boston Red Sox crushed three grand slams and narrowly missed a championship-series record, with 21 runs scored over a two-game span. Going into Game 4, our forecast model gave the Astros just a 34 percent chance of advancing to their third World Series in the past five seasons.

But a lot can change in just a few games. After those two rocky performances, Houston clamped down on Boston’s hitters, cranked up the offense and won Games 4 and 5 by margins of 9-2 and 9-1 — not far off from the 21-8 run differential they suffered in Games 2 and 3. That 28-run turnaround — from a minus-13 margin across two games of a playoff series to plus-15 over the next two games — was the second-most abrupt in the history of the MLB postseason, trailing only the Red Sox’s 33-run turnaround in Games 3 and 4 of the 1999 American League Division Series.

The quick about-face now has Houston sitting at an 82 percent chance of besting Boston for the pennant, with a 37 percent chance of winning the World Series for good measure. And for the Red Sox’s part, they must now win two elimination games in a row on the road, starting with tonight’s Game 6 duel between Nathan Eovaldi and Garcia.

So how did the Astros flip things around on Boston so decisively? One clear factor was the reemergence of Houston’s big bats. In Games 2 and 3, the Astros collectively hit for a .600 OPS — for comparison’s sake, their season average was .783, and Boston allowed a .749 mark — and only 29 percent of their plate appearances came with any runners on base (with only 7 percent coming with runners in scoring position). Along the way, the normally dangerous group of Yordan Álvarez, Michael Brantley, Alex Bregman, Carlos Correa and José Altuve were held in check with a paltry .282 OPS, as Boston’s pitchers — particularly Game 3 starter Eduardo Rodríguez — made it through the scary Houston lineup with little trouble.

But over the two games that followed, the Astros did the kind of damage that opposing pitchers have come to fear from them. Houston rebounded for an .864 OPS across Games 4 and 5, with Álvarez, Brantley, Bregman, Correa and Altuve delivering a 1.026 effort by themselves. (Álvarez in particular dominated Game 5, going 3-for-5 with a double, a home run and three RBIs.) Unlike in the previous two contests, 48 percent of Houston’s plate appearances saw runners on base, with 34 percent coming with runners in scoring position. The Astros didn’t hesitate to cash in on those chances, either, hitting .458 with RISP and .643 specifically with RISP and two outs.

And while Houston’s shaky pitching has been a huge story throughout the ALCS, as Lance McCullers Jr., the team’s best regular-season pitcher by wins above replacement, is sidelined with a muscle strain, the Astros responded to the poundings of Games 2 and 3 in impressive fashion. Houston’s relief pitching — one of its biggest question marks during the regular season — picked up the slack after Zack Greinke lasted only 1⅓ innings in Game 4, with the bullpen tossing 7⅔ innings of shutout ball the rest of the way, and Game 5 starter Framber Valdez was stellar over eight innings of work, allowing just one run, three hits and a .465 OPS. Although Rafael Devers continued to hit, Houston’s pitchers found a way to neutralize J.D. Martinez, Kyle Schwarber, Alex Verdugo and the red-hot Kiké Hernández after offering little resistance to them early in the series.

The Astros are hardly home free now, of course, as they turn back to García (who has a wait-that-can’t-be-right-oh-wow-it-is 24.55 ERA in the postseason this year) as Game 6’s starter. Valdez’s gem bought Houston’s pen — which used four pitchers in Game 2 and five apiece in Games 3 and 4 — a badly needed reset for the closing stages of the series, but there are plenty of innings left to be filled.

Even so, the Astros have flipped their fortunes completely around over the past few games, in a way few teams from history ever have. They regained their form at the plate, cooled off Boston’s hottest bats and overcame their own pitching problems. Houston’s return to the Fall Classic could make for a complicated World Series narrative — to say the least — but they have certainly earned this ALCS upper hand the hard way.

Check out our latest MLB predictions.