Giants starter Jeff Samardzija was responsible for Alonso's second-inning home run, an opposite-field shot to left, but allowed just one other hit and struck out three in his 2 2/3 innings.
"In Spring Training, you're going to go in there and attack, and try to avoid the walks," Samardzija said. "As a whole, I'm really happy with getting ahead in the count and putting guys away. No walks, so for Spring Training, it's a good outing."
Daniel Gossett, Oakland's No. 7 prospect per MLBPipeline.com, did his part with two scoreless innings, weaving his way through a Major League regular-heavy Giants lineup with ease. San Francisco was held to three total hits.
"I'll tell you what, he's really impressing," A's manager Bob Melvin said of Gossett. "He's throwing the ball over the plate. They basically have their A-team out there, too. Our reports were really good on him. He comes as advertised."
A's non-roster outfielder Kenny Wilson added a three-run shot in the seventh.
Giants up next:Clayton Blackburn, who has had one strong outing and a subpar performance this spring, will start Saturday against the Royals in Surprise at 12:05 p.m. PT. Blackburn threw two scoreless innings on Feb. 24 against Cincinnati, then yielded three runs in two innings Monday against the Reds. Right-hander Kyle Crick also is scheduled to pitch.
Athletics up next: Center fielder Rajai Davis will be in the leadoff spot Saturday when the A's welcome in his former Indians team for a 12:05 p.m. PT matchup at Hohokam Stadium. Left-hander Sean Manaea gets the start for Oakland, his second this spring.