Boston was trailing the Detroit Tigers 5-1 and looked all but certain to fall behind 2-0 in the best-of-seven American League championship when Red Sox designated hitter David Ortiz came to bat in the bottom of the eighth inning.
The 37-year-old Dominican slugger was up to the occasion, smacking a grand slam to tie the score.
Koji Uehara held the visitors scoreless in the top of the ninth and catcher Jarrod Saltalamacchia went on to hit a one-run single that allowed the Sox to salvage a split at home.
The series shifts to Detroit on Tuesday for the next three games.
It was the first-ever post-season grand slam for Big Papi, one of the standouts of the Red Sox's 2004 playoff campaign that brought Boston its first World Series triumph in 86 years.
Tigers starter Max Scherzer allowed only two hits and one run in seven innings, but Detroit's bullpen struggled.
The Tigers went through three pitchers in the bottom of the eighth before turning to closer Joaquin Benoit, who couldn't handle Ortiz.
Game 3 will pit the Tigers' Justin Verlander against John Lackey for the Red Sox. EFE