By Steve Ginsburg

SAN FRANCISCO (Reuters) - The San Francisco Giants moved a step closer to claiming a second title in three years by blanking the punchless Detroit Tigers 2-0 on Thursday to extend their World Series lead.

Detroit was held to two hits by Giants starter Madison Bumgarner and relievers Santiago Casilla and Sergio Romo, failing to reach second base after the second inning as the Giants opened a 2-0 advantage in the best-of-seven series.

Hunter Pence was involved in both Giants runs, racing home from third on a double-play in the seventh inning and then lofting a sacrifice fly in the eighth to score Angel Pagan.

The series now shifts to Detroit for the next three games, if necessary, where the Tigers will be desperate to open their account in front of a packed home crowd.

Bumgarner, who was yanked from the starting rotation after a poor performance in Game One of the National League Championship Series, gave up only two hits over seven innings to earn the victory.

The Giants, who banged out 11 hits in an 8-3 victory in the series opener on Wednesday, managed only five hits against four Tigers pitchers but were able to take full advantage of their few chances.

Detroit's Doug Fister continued his brilliant postseason pitching, but was forced to absorb the loss after giving up four hits and one run over six innings.

He surrendered that run in the seventh but pitched to only one batter when Pence had a lead-off single and Tigers manager Leyland exchanged Fister for southpaw Drew Smyly, who walked Brandon Belt.

Gregor Blanco followed with a bunt that hugged the line to load the bases. Crawford, the third left-handed hitter in a row, then hit into a double-play but Pence scored from third.

An inning later, three walks loaded the bases, allowing Pence to hit his run-scoring sacrifice fly to right.

The Tigers lone offensive threat came in the second when Delmon Young doubled into the left-field corner but a tardy Prince Fielder, trying to score from first, was nailed at the plate on a relay throw to catcher Buster Posey by second baseman Marco Scutaro.

(Editing by John O'Brien)