Neither Cain nor his teammates, though, were in a mood to celebrate. They were too concerned over rookie reliever Joe Martinez, who was hit in the head by a Mike Cameron line drive with two outs in the top of the ninth.
Martinez, who remained conscious and walked off the field, was taken to a local hospital for a CT scan.
The incident put a damper on what had been a spectacular day for Cain and the Giants.
"Everything was going good," Cain said in a somber clubhouse. "Bengie and I were clicking well. We were just getting ahead of them with offspeed pitches and fastballs. We were just trying to keep them off balance. Defense played a huge role in this game today."
Winn and Sandoval, in particular, made huge defensive plays, stealing multiple hits from the Brewers.
But Cain's greatest support came in the form of singles and doubles zipping throughout AT&T Park.
After three scoreless innings, the Giants struck for two runs in the fourth and three in the fifth, giving Cain a 5-0 lead.
"It was good," Cain said. "It was good to get an lead early. My biggest thing was just to keep staying focused and put up a zero every inning and just limit the damage in the one inning I got in trouble."
Cain gave up only four hits, three singles and a double. He struck out five and walked only two. He threw just 90 pitches, and 61 of those were strikes. That qualifies as efficiency, which was his goal.
"It was nice," he said. "It was good. I was definitely just trying to get these guys to swing early and put the ball in play early. We know that they're going to be aggressive. It worked out well."
More often than not the past two seasons, Cain has had little support. In 2007 he went 7-16 with a 3.65 ERA. Last season he went 8-14 with a 3.76 ERA.
If Thursday's game is any indication, Cain's luck may be changing. In the fourth inning, Lewis led off with a double and scored when Molina drove a Manny Parra pitch off the right-field wall for another double.
Then Molina took third on a wild pitch and scored on Rowand's single to center. Just like that, Cain had a 2-0 lead.
In the fifth, Cain helped himself with a leadoff walk, and Winn singled him to second. Edgar Renteria then grounded to third baseman Craig Counsell, who stepped on third, forcing Cain. But when Counsell threw wildly to first, Winn raced all the way around to score on the error, making it 3-0.
When Parra walked Lewis, his day was done. Enter right-handed reliever Mark DiFelice.
Molina greeted DiFelice with a two-run double to left-center, scoring Renteria and Lewis and pushing the Giants' lead to 5-0.
The Brewers finally got to Cain for a run in the seventh. J.J. Hardy led off with a single, and Cain walked Cameron. After Corey Hart reached on a fielder's choice, moving Hardy to third, Jason Kendall launched a sacrifice fly to center. But Cain ended the rally by striking out pinch-hitter Chris Duffy.
Cain said that he felt good about the way he was throwing coming out of Spring Training. Thursday's victory served as confirmation, and it gave the Giants a 2-1 series win over the Brewers, who beat them all six times last year.
"That's definitely a great way to start off the season," Cain said. "Got a long ways to go. Just kind of keep it running that way."