Josh Harrison stroked a two-run single and Starling Marte used his bat and his legs to produce two key runs as the Oakland Athletics defeated the visiting San Francisco Giants 4-1 on Friday in the opener of a three-game series.

Right-hander James Kaprielian (7-4) combined with four relievers on a five-hitter, helping Oakland, the second-place club in the American League West, open a nine-game homestand with its second win over San Francisco in four meetings this season.

Harrison gave the A's a lead they never relinquished when he followed a Jed Lowrie walk and Yan Gomes double with a one-out looper into center field to end a scoreless duel in the fourth inning.

Mike Yastrzemski got the Giants back within 2-1 in the fifth with his 19th home run of the season. But that was the last of the San Francisco scoring against Kaprielian, Jake Diekman, Yusmeiro Petit, Sergio Romo and Lou Trivino.

Trivino handled the ninth inning for his 21st save.

Making his first career start against the National League West-leading Giants, Kaprielian went five innings, allowing one run on three hits. He walked four and struck out four.

The game remained a one-run affair until Marte doubled down the right field line with two outs in the seventh inning, scoring Mark Canha.

Jose Alvarez replaced Zack Littell on the mound for the Giants at that point, and before the left-hander had even thrown one pitch, Marte took off for third during the pitcher's stretch.

Alvarez saw it coming, stepped off and threw to third, but the ball and Marte arrived at about the same time, and Giants third baseman Wilmer Flores couldn't handle the throw. The ball rolled down the third base line, allowing Marte to score, making it 4-1.

Giants starter Alex Wood (10-4) worked five innings, during which he was charged with two runs on five hits. He walked two and struck out nine.

San Francisco had been 11-0 when Wood started immediately following a Giants loss, but that streak ended. The Giants were beaten in their final game of a 7-2 homestand by the New York Mets on Wednesday.

Harrison and Gomes had two hits apiece for the A's, who collected just six hits.

Alex Dickerson had two singles for the Giants, who opened a nine-game road trip.

--Field Level Media