Peralta, 24, went six innings for the Brewers (10-12), giving up eight hits and five runs with two walks and two strikeouts. But Peralta allowed just one home run on the warm and breezy afternoon, with Mariners catcher Mike Zunino cracking his first long ball of the spring in the sixth.
Logan Schafer, Khris Davis, Mark Reynolds and Juan Francisco each cleared the wall for the Brewers in the first four frames, with Reynolds and Francisco going back-to-back leading off the fourth.
Davis and Francisco now have three homers, Reynolds hit his second and Schafer launched his first long ball of the spring. Schafer went 2-for-4 to raise his spring average to .366, while Davis, Reynolds and shortstop Jeff Bianchi each had two hits as well.
Beavan hadn't allowed a home run in his previous 12 2/3 innings this spring, but said Wednesday's barrage wasn't just about the warm Arizona air.
"I've got to make better pitches," said the 25-year-old, whose ERA climbed to 4.91. "I thought three of the four were doubles, but I still have to make better pitches. You kind of know what you're dealing with out here. But I was a little off today and just couldn't recover the whole game."
Mariners reliever Ramon Ramirez replaced Beavan with two out in the sixth and Peralta promptly greeted his first pitch with a two-run poke into Seattle's bullpen behind the left-field fence.
"First one of the year feels good," Peralta said with a laugh.
Try first one ever, in a Major League regular season or exhibition game. Peralta did hit one home run at Double-A Huntsville in 2011.
Of his pitching, he said, "It feels good. The third inning, I was a little out of rhythm, trying too hard with the slider. Once I found a rhythm, I was fine. I just got my work done and got my pitch count where I wanted to."
Reynolds' home run was his second in as many days. He leads the Brewers with 11 RBIs.
"The timing is coming back, and that's the hardest thing to regain," he said. "You see some guys start off hot because they played winter ball, but I haven't taken a swing since September. It's coming back to me."
Mariners shortstop Brad Miller continued his own Cactus League tear with a 3-for-4 day that included his third and fourth triples of the spring. Miller already leads Seattle with four home runs and is hitting .447 in 13 games.
Second baseman Robinson Cano returned from a five-day absence to deal with a family issue in the Dominican Republic and went 1-for-4 with an RBI single in the third and a run-scoring groundout in the seventh, putting his spring average at .556 (15-for-27) with eight RBIs.
Kyle Seager hit his first Cactus League home run with a solo shot in the seventh off Brewers reliever Will Smith in a 2-for-4 day.
Right fielder Michael Saunders increased his team lead in RBIs to 12 with a second-inning sacrifice fly and first baseman Justin Smoak laced a run-scoring double that plated Cano in the third.
Up next: Felix Hernandez will throw in a Minor League game at the Peoria Complex on Thursday, leaving Erasmo Ramirez to take the Cactus League start against the Cubs in Mesa, Ariz., in a 1:05 p.m. PT game on MLB.TV. Hernandez made the choice to pitch at home rather than taking the trip to Mesa and will have one more Cactus League start next week against the Royals. Ramirez appears locked into Seattle's rotation and is 2-0 with a 1.42 ERA in four spring outings.