(Reuters) - The San Francisco Giants blasted three home runs and overcame a shaky start from Barry Zito to beat the Cincinnati Reds 8-3 on Wednesday and set up a one-game showdown for a place in the National League Championship Series.

After losing the opening two games of the division series at home, the Giants fought back with a pair of road wins to set up a decisive fifth game on Thursday at Cincinnati's Great American Ball Park.

Gregor Blanco and Pablo Sandoval each crushed two-run homers while Angel Pagan added a solo shot to stun the capacity crowd that had been expecting to celebrate the Reds' first trip to the NLCS since 1995.

Zito allowed four hits, fours walks and two runs in 2-2/3 innings and it was Tim Lincecum who came to the rescue for the Giants, registering the win after allowing just one run and two hits in 4-1/3 innings of sparkling relief.

(Reporting by Steve Keating in Toronto; Editing by Frank Pingue)