Giants 8, Athletics 6: Brandon Belt drove in three runs and Angel Pagan scored three times as host San Francisco jumped out to a seven-run lead and held on to take the series opener between the Bay Area rivals.

Belt had an RBI single in a two-run first inning and added a bases-loaded walk during a four-run third. The Giants benefited from five free passes in the third, culminated by former Athletics star Barry Zito receiving a bases-loaded walk as well.

Hector Sanchez, who was playing in place of Buster Posey, collected two hits and two RBIs as San Francisco won its second straight and fifth in seven outings.

Zito (3-1), who left Oakland to sign a seven-year, $126 million contract, exited after 5 1/3 innings. The left-hander improved to 2-4 in his career against the Athletics, but yielded four runs on five hits while striking out five.

Josh Donaldson homered and drove in five runs and Cliff Pennington had an RBI single as Oakland closed to within 8-6, but the Giants' bullpen closed the door. Four relievers combined to strike out six over three scoreless innings, capped by Santiago Casilla retiring the side in the ninth for his 10th save of the season.

Jarrod Parker (1-2) once again struggled with his control. After yielding nine walks in his previous two starts, Parker allowed four free passes to go along with six runs on four hits in two innings.

GAME NOTEBOOK: Pagan went 1-for-2 with three walks to extend his hitting streak to nine games. He has hit safely in 29 of his last 30 contests. ... P Brad Penny agreed to terms on a minor league contract with the Giants. He will report to extended spring training on Monday. ... Donaldson also had a gem in the field after he made a diving stop on Brett Pill in the seventh inning.