Giants 8, Padres 7: Joaquin Arias had three hits and three RBI as visiting San Francisco staved off a late rally to continue its dominance of San Diego.

Jose Mijares (1-0) earned his first National League win in relief of Barry Zito, who gave up four runs over four innings. Jeremy Affeldt allowed two runs in the ninth before Clay Hensley struck out pinch hitter Mark Kotsay with one on for his third save.

Trailing 4-1 in the fifth, the Giants moved ahead with four runs in the frame and added two in the seventh. Hunter Pence added an insurance run with an RBI double in the ninth to keep San Francisco one-half game ahead of Los Angeles in the National League West.

San Francisco has won 14 of its last 19 games in San Diego and 19 of 25 overall against the Padres.

Arias gave the Giants an early lead with a solo homer in the second before the Padres tied the game in bottom half and took a 4-1 lead on Chase Headley’s three-run blast in the third.

Arias capped the Giants’ four-run rally in the fifth with an RBI single off Eric Stults, who allowed five runs on nine hits over six innings.

The Padres pulled within a run when Carlos Quentin led off the sixth with his 13th homer, but the Giants answered with two runs in the seventh on Buster Posey’s sacrifice fly and Arias’ RBI single off Brad Brach (1-3).

San Diego has been outscored 36-9 during its current five-game losing streak.

GAME NOTEBOOK: The Giants have won 11 of their last 15 road games, outscoring opponents by a 111-50 margin. … The Padres optioned RHP Ross Ohlendorf to Triple-A Tucson. … Headley has hit .328 (21-for-64) with eight home runs and 24 RBI in 14 games this month. … Zito was seeking his first win at Petco Park since 2008. … Posey went 3-for-4 and has hit safely in 28 of his last 32 games.