Buster Posey homered in the eighth inning and Matt Cain teamed with three relievers on a two-hitter as the San Francisco Giants maintained their lead in the National League West with a 1-0 triumph over the Chicago Cubs.

Juan Uribe went 2-for-4 for the Giants, who have won eight of their last 10 road games.

San Francisco entered with a one-half game division lead over San Diego. It threatened in both the second and fifth innings but was unable to break through against Carlos Zambrano, who had won each of his previous five starts.

With one on and one out in the second, Pablo Sandoval and Uribe hit back-to-back singles to load the bases for Cain, who struck out to end the inning.

Zambrano, who is 6-0 with a 1.42 ERA over his last nine outings, also found the bases loaded with two outs in the fifth before inducing a flyout by Posey.

Zambrano departed after allowing three hits, walking five and hitting a batter while striking out eight in six innings.

Cain also worked six frames, limiting the Cubs to a pair of singles and a walk. The 25-year old hit a batter and struck out two.

The Giants finally got on the board with one out in the eighth, when Posey deposited a 3-1 offering from Andrew Cashner (2-6) over the center-field wall for his 15th blast of the season and a 1-0 advantage.

Ramon Ramirez (1-3) and Sergio Romo each worked a perfect inning before Brian Wilson set down the side in order in the ninth for his 44th save in 48 opportunities.

Blake DeWitt and Kosuke Fukudome each singled for Chicago, which had its six-game winning streak snapped.