Miguel Cabrera gave the Detroit Tigers their first lead of the World Series when he homered off Matt Cain in the third inning of Game 4.
With the Giants holding a 1-0 lead, Cabrera stepped in with Austin Jackson on second and took an outside changeup the other way. Hunter Pence appeared to have a beat on the ball, but the wind-aided fly carried into the right-field bleachers at Comerica Park.
The American League-champion Tigers, trailing 3-0 in the series, had not scored since the ninth inning of the opener.
The Giants are riding a six-game winning streak and had not trailed since losing Game 4 of the NL Championship Series to the Cardinals, a span of 56 straight innings -- four shy of tying the record for a single postseason.
Twenty of the previous 23 teams to hold a 3-0 World Series advantage have completed their sweeps, while the other three have finished the series in Game 5.
Cain, who is trying to become the third pitcher in MLB history to earn a victory in three clinchers in a single postseason, shook off a two-out walk to Cabrera in the first inning and retired three straight after Delmon Young led off the second with a line-drive single.
San Francisco took the lead in their half of the second when Hunter Pence hit a ground-rule double off Max Scherzer and raced home on Brandon Belt's triple to right field.
Scherzer stranded Belt at third and left runners on the corners an inning later by getting NL batting champion Buster Posey on a flyout to center.