Yordan Alvarez had three hits and three RBIs for Houston, which can clinch its third pennant in five years with a victory in Game 6 at home on Friday night. The Red Sox need a win to force a deciding seventh game on Saturday.
One day after the Astros scored seven runs to break a ninth-inning tie, they hung another crooked number on the Fenway Park scoreboard, chasing Chris Sale while scoring five runs in the sixth. Alvarez, who homered in the second and singled in the fourth, had a two-run double to break things open.
That was plenty for Valdez, who extended the staff's shutout streak to 14 straight innings before Rafael Devers homered with one out in the seventh - one of just three hits for Boston. The left-hander departed after retiring the Red Sox in order in the eighth - the longest outing for any starter this postseason.
In all, Valdez gave up one run on three hits, one walk and a hit batter, striking out five. He was also the first opposing pitcher to last eight innings in a postseason start at Fenway since Cleveland's Charles Nagy went eight in the 1998 Division Series.
Ryne Stanek pitched a perfect ninth while the rest of Houston's relievers rested. Astros starters had not lasted three innings all series, pitching to a 18.90 ERA in the first four games and giving up 10 homers - including a record three grand slams.
Valdez was not much better, allowing two earned runs in 2 2/3 innings in Game 1.
But retired the first 12 batters on Wednesday - eight on grounders, four on strikeouts. Devers singled to lead off the fifth, then Valdez bounced the next pitch off J.D. Martinez's leg. The Astros escaped when Hunter Renfroe grounded into a double play and Alex Verdugo bounced out to first.
Sale started almost as well, allowing just two hits - both to Alvarez - in his first five innings. But he walked Jose Altuve to start the sixth, then Michael Brantley nubbed one toward third. Devers fielded it and made the throw in time but Schwarber dropped it at first; after sliding into second, Altuve popped up and took off for third, which was uncovered.
Brantley moved up to second on a groundout to the pitcher, then Alvarez doubled to left, scoring two to make it 3-0 and chasing Sale. Ryan Brasier struck out Carlos Correa before giving up an RBI double to Yuli Gurriel and a two-run single to Jose Siri that made it 6-0.
Brantley added an RBI single in the seventh, and Gurriel singled in two more in the ninth.
Sale was charged with four runs - two earned - on three hits and two walks, striking out seven in 5 1/3 innings.
The Red Sox had won seven straight postseason games at home - dating to the 2018 ALCS - before blowing an eighth-inning lead on Tuesday night. They had never lost back-to-back postseason games under manager Alex Cora.
The teams take Thursday off before resuming with Game 6 on Friday night in Houston. Nathan Eovaldi, who won Game 2 but came on in relief and lost in Game 4, will start for Boston. Houston manager Dusty Baker has not identified a potential starter.
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