BOSTON _ J.D. Martinez landed the first staggering punch, launching one over the Green Monster _ a three-run shot off J.A. Happ that sent Red Sox Nation into an early frenzy.
Boston would open a five-run lead in the AL Division Series opener, but its rickety setup relief teetered on the verge of giving it all back.
Aaron Judge crushed a ninth-inning, leadoff homer off Craig Kimbrel, putting a sellout crowd on edge.
But the Red Sox closer rebounded to strike out the side _ including Giancarlo Stanton _ to finish a 5-4 Boston victory before 39,059 fans.
It took scheduled Game 3 starter Rick Porcello to help restore order in the Back Bay, getting two quick outs in the eighth before Kimbrel's four-out save, striking out Luke Voit to end it.
In dropping the first game of this best-of-five against their ancient rivals, the Yankees might have also lost switch-hitting center fielder Aaron Hicks.
Following a fourth-inning leadoff single, Hicks exited due to right hamstring tightness, with Brett Gardner taking over in center field.
Hicks dealt with left hamstring tightness in late September, but his return _ along with Didi Gregorius (torn ligament, right wrist) and Judge (fractured right wrist) _ before October had restored the Yankees lineup to full strength.
Yankees lefty Happ had performed as well as any visiting starter to Fenway Park in recent years.
And yet, the Red Sox's fast strike against him was a stunning first-round blow.
Having pitched to a 1.99 ERA against Boston during four regular-season starts in 2018, the veteran was lifted in the third inning, charged with five earned runs on four hits and a walk.
Granted a 5-0 lead after three innings, Red Sox lefty ace Chris Sale eventually yielded to five Red Sox relievers, and it was a bumpy ride.
Both of Sale's inherited runners in the sixth scored, on a single by Voit and a fielder's choice by Gregorius.
But with the bases loaded and the crowd standing, Brandon Workman came back from a 3-and-1 count to strike out rookie Gleyber Torres swinging over a curveball, ending the inning.
In the seventh, the Yankees loaded the bases with none out, but settled for one run.
Matt Barnes recorded a huge first out, striking out Giancarlo Stanton on a breaking ball. Voit's RBI groundout made it 5-3, but that's all the Yanks could get.
Sale hadn't pitched more than 42/3 innings since Aug. 12, gradually building back after a second stint on the 10-day disabled list with left shoulder inflammation.
"I know there's been a lot of talk about it," Yankees manager Aaron Boone said before the game, referring to questions as to Sale's October effectiveness. "But we'll prepare for the great pitcher and see what we get.
"He's obviously pitched really well against us ... he's a great competitor," Boone said. "He's going to be, on some level, very tough for us."
Sale mostly coasted through five innings, striking out eight batters and yielding three hits _ all singles _ and two walks.
But singles by Judge and Stanton chased Sale in the sixth, at the 93-pitch mark. And a rocky parade of Red Sox relievers began.
After striking out Betts to open the first inning, Happ yielded a single to Andrew Benintendi, a budding Yankee killer, who stole second.
Steve Pearce walked and Martinez rocketed one over the Monster's left corner, giving Boston a 3-0 lead.
Happ retired the next five consecutive batters but his night ended in the third, after Betts doubled off the Monster in left-center field and Benintendi reached on a bunt single.
It was an aggressive move by Boone, getting Happ after 44 pitches.
But the next batter was Pearce, a .344 hitter with six home runs in 32 at-bats against Happ, who'd surrendered a grand slam to Pearce here on Sept. 28.
"I think if I don't start Pearce, I might get fired," Red Sox manager Alex Cora said before the game. "He hits the ball out of the ballpark."
Both inherited runners scored against Yanks reliever Chad Green, on a Pearce single and Xander Bogaerts sacrifice fly.
