"You can say it's spring or say whatever, but you still have to hit the ball and play the game," said Morse. "I think half of the way we're playing is because guys are relaxed and confident and they're believing in their abilities. And everybody is playing within their abilities. It's something we have to remember, bottle up and carry over to the season."
The Brewers played a little long ball of their own with three home runs, including the go-ahead blast by Minor League outfielder Cole Garner off Seattle reliever Charlie Furbush that gave Milwaukee a 7-6 lead in the top of the eighth.
First baseman Hunter Morris and designated hitter Khris Davis also went deep in the first three innings off Seattle starter Blake Beavan. Davis, a left fielder making the most of Ryan Braun's absence in the World Baseball Classic, hit his second home run in the past two days with a two-run blast in the third.
"He's doing well for himself," said Brewers starter Mike Fiers, who helped his own case with another solid start.
Fiers, one of the four pitchers vying for three open spots in Milwaukee's starting rotation, went 3 1/3 innings with two runs, three hits, one walk and three strikeouts. His first run came courtesy of a single lost in the sun by left fielder Caleb Gindl, before giving up a leadoff home run to Morse in the fourth.
Fiers, 27, threw 49 pitches in his third appearance as his spring ERA now stands at 3.24. He worked hard over the offseason to build strength after a late-season fade tarnished his strong start following his promotion from Triple-A.
"It wasn't extra work -- it was just getting my baseball body back," Fiers said. "People don't realize how much you have to do to get back into midseason form."
Second baseman Rickie Weeks went 3-for-3 with three singles and a run scored for the Brewers, who were playing shorthanded with 12 players -- nine from their 40-man roster -- in the World Baseball Classic and several others getting the day off.
Beavan pitched three innings for his second straight outing for Seattle, but gave up six hits and three runs in the process.
The Mariners scored four runs off young reliever Johnny Hellweg in the fifth, the big blow coming on Morales' two-run blast. Center fielder Franklin Gutierrez doubled and scored in the same inning and made a long running catch in center field in the top of the same inning to continue his strong spring.
"Well, we wanted to see him against a really good lineup, which we did," Brewers manager Ron Roenicke said of Hellweg. "He's got to understand you can't make mistakes to Major League hitters. When he's down in the zone, nobody can hit him, and that inning, it was all up and guys don't miss it."
Milwaukee tied the game back up at 6-6 with three runs in the top of the seventh off Seattle's Josh Kinney.
Brewers up next: Right-hander Mark Rogers faces an important start Thursday against the D-backs at Maryvale Baseball Park. He was bumped to Minor League camp for his last turn through the rotation, a move the Brewers hoped would help Rogers build some confidence amid a case of springtime dead arm. Rogers, a former first-round Draft pick whose rise was delayed by multiple arm injuries, is out of options and one of three young pitchers competing for a spot in Milwaukee's starting rotation. Also, expect Alex Gonzalez back in the lineup Thursday after getting Wednesday off. The question is which position he'll play -- he will appear at first base, third base and shortstop before the month is out.