Hernandez allowed one hit in six scoreless innings. He struck out six and walked one. He struck out the side in the third inning.
"I was throwing all my pitches, and they were working pretty good," Hernandez said.
The Brewers got their first hit of the game on Caleb Gindl's single off Hernandez with one out in the fourth inning. Milwaukee brought none of its regulars to Tucson. It was a split-squad game for the Brewers, who were also playing the Kansas City Royals in Surprise.
Ramon Morla's two-run single with the bases loaded gave the Mariners a 2-0 lead in the second inning. Dustin Ackley then smacked an RBI double for a 3-0 lead.
The Mariners' Alex Liddi hit a two-run home run in the eighth inning for a 5-1 lead. Ackley had three doubles. Seattle added two runs in the ninth.
For the Brewers, starter Marco Estrada allowed three runs and five hits in three innings. He struck out two and walked two.
"I felt pretty good," said Estrada, who has been filling in for starter Shaun Marcum, who has been limited because of shoulder inflammation. Estrada could replace Marcum if he isn't ready for the season.
"The heat's a little stronger here than it is down in Phoenix," Estrada added. "I felt good. That second inning got me going a little bit. It was a little rough. They hit a couple mistakes I made, but overall I felt really good. I thought I kept the ball down. Not too many balls were hit hard. I had a lot of ground balls today. I'm happy with the way I threw."
Milwaukee scored its run in the seventh inning after Brooks Conrad doubled and center fielder Daniel Carroll lost the ball in the sun. Conrad scored after a flyout and a groundout.
The Mariners are nearing their trip to Japan. They leave on Thursday and will likely take 30 players to play two exhibition games against Japanese teams before opening the season on March 28 against the Oakland A's at the Tokyo Dome.
The Mariners and Brewers were playing at the former Spring Training site of the Chicago White Sox and Arizona Diamondbacks. Tucson baseball officials have worked to organize spring games in the city since the teams moved to Phoenix.
Up next for the Mariners: Blake Beavan, Lucas Luetge, Tom Wilhelmsen, Hong-Chih Kuo and Oliver Perez are scheduled to pitch against the Chicago White Sox in Glendale on Saturday, live on Gameday Audio. For the White Sox, Jake Peavy will start.
Sarah Trotto is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.