The Twins have won all of his past seven starts.
"That's one thing I try to do, get into that rhythm, staying aggressive, attacking hitters," said Baker, who helped keep his club 3 1/2 games ahead of the White Sox in the American League Central.
"Obviously, the defense appreciates it. It allows me to throw strikes on a more consistent basis."
During this streak, Baker has a 3.02 ERA with 33 strikeouts. He also won for the third time in his last four road starts after having just one win in his first nine.
Mauer had three hits, including an RBI single in the first and a run-scoring double in the seventh.
Mauer became the third player in the AL to reach 40 doubles this season. It also was his 18th three-hit game.
Valencia added a two-run triple in the Twins' breakout three-run sixth.
"He was able to throw whatever pitch he wanted for a strike, pretty much all night," manager Ron Gardenhire said of Baker. "He was able to throw his fastball strike one and also spin his breaking ball strike one to get them off his fastball. When you do that, you're in command of the ballgame."
Randy Flores, claimed off waivers from Colorado on Wednesday, made his debut in the seventh, taking over for Baker. He gave up an infield hit to Ichiro Suzuki, loading the bases, but induced Chone Figgins to ground out.
However, Flores pitched into a jam in the eighth, loading the bases with no outs. That's when Matt Guerrier earned his share of the victory.
Guerrier got Franklin Gutierrez to pop out into foul territory before Adam Moore hit into a double play. Guerrier had given up a two-run homer Thursday in Texas to Vladimir Guerrero.
"No one wants to be out there more than Matty after [Thursday], so it was good for him and good for us," Baker said. "It was a big situation. It always seems like there's some adversity at some point during the game and he handled himself very well."
Gardenhire said Guerrier "was absolutely huge tonight. We [made an error] and normally that comes back to haunt you, but Matty got three big outs for us and kind of gave us a little breathing room."
The Twins led by just a run, 2-1, in the sixth when Michael Cuddyer singled with one out. Delmon Young then singled off the left-field wall, just missing a home run. Cuddyer held at third, but then Valencia crushed his triple into the right-center gap.
Valencia later scored on Alexi Casilla's infield single.
The Twins applied immediate pressure to Mariners starter Jason Vargas (9-7), scoring a run in the first and second innings.
Denard Span opened the game with a single to center. Orlando Hudson followed with a double into the left-center gap. Span raced around third, but was thrown out on a close play at home.
Hudson took third on the throw and scored on Mauer's bloop single to left.
In the second, Valencia walked and Jason Repko singled. Vargas forced Valencia at third on Casilla's bunt attempt.
The runners moved up on a passed ball and Repko scored on Drew Butera's sac fly to right.
"You got to have it. You have to spread it out," Gardenhire said. "We did that pretty decently tonight."
The Mariners got one back in the third. Ichiro opened with a triple into the right-center gap. He scored on Figgins' groundout.