MILWAUKEE (AP) The first full season of the Milwaukee Brewers' rebuilding era began with a blowout loss.

Outfielder Ryan Braun thinks this is a perfect time for the younger members of the team to learn a valuable lesson.

Scooter Gennett and Jonathan Villar hit homers off San Francisco's Madison Bumgarner, but the Giants' hitters backed their ailing ace in a 12-3 victory in an opener on Monday.

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The Giants hit three straight homers in the eighth off reliever Ariel Pena.

''Everything at this level feels like it's magnified a little bit,'' said Braun, who was 1 of 4. ''But for everybody it's something if you've played the game long enough you understand you have to be good at turning the page whether it's from a good game or a bad game.''

Denard Span homered and drove in five runs in his San Francisco debut. He hit a three-run shot with two outs in the eighth inning and Joe Panik and Buster Posey followed with solo shots off Pena.

''That inning we hit the three homers that says it right there,'' said third baseman Matt Duffy, who helped out with a homer and four RBIs. ''I'd say contagious is a good word right there.''

It marked the first time the Giants had connected for three straight homers on opening day.

It was the first time any team had done it in an opener since the Padres in 1997. The only other time a team to hit three straight homers in an opener was the 1948 Red Sox.

The Giants scored quickly against Wily Peralta and bailed out the ailing Bumgarner, who left after the fifth with a four-run lead. The left-hander allowed five hits, five walks and three runs.

The 2014 World Series MVP looked out of sorts after allowing a homer to deep right in the second to Scooter Gennett, a career .124 hitter against lefties.

In homering off Bumgarner, Gennett accounted for himself well in trying to prove that he can play full-time against left-handed pitching.

''Just going out there and basically doing what I can and that's putting the bat on the ball and swinging at good pitches,'' Gennett said. ''That's what I can control.''

Villar, the new starting shortstop acquired from Houston in the offseason, homered off Bumgarner in the third in his Brewers debut.

AILING ACE

Manager Bruce Bochy said an illness was going around the Giants clubhouse, and that Bumgarner had been taking medicine to get ready for his third straight opening day start. Bumgarner had a fever and chills on Sunday night, the skipper said.

BAD START

For Milwaukee, Peralta was tagged for five runs and six hits in four innings.

''They just put some good at-bats against him. What they're good at it is putting the ball in play on tough pitches with two strikes,'' manager Craig Counsell said.

UNSUAL OPENER

This was the first time that San Francisco had opened a season in Milwaukee. The Giants might remember this trip for reasons other than baseball, too.

On Sunday, the team plane arrived and pulled into the Milwaukee airport next to an aircraft belonging to the campaign of Republican presidential candidate Donald Trump. The Wisconsin presidential primary is Tuesday.

Light snow flurries fell outside Miller Park during the opener, though the stadium's retractable roof kept fans warm and dry.

TRAINER'S ROOM

Brewers: P Matt Garza's turn on Wednesday will be skipped after the right-hander left a spring training game on Saturday with shoulder tightness. Counsell said Taylor Jungmann will be moved up to Wednesday, but that Garza could still pitch over the weekend.

UP NEXT

Brewers: RHP Jimmy Nelson takes the hill after a solid spring training, going 2-1 with a 1.17 ERA in four starts.