Saarloos pitched 3 2/3 shutout innings after Justin Duchscherer left with a hip injury and the A's held on for a 3-2 win.
"That's the job that he was brought up here to do," A's manager Bob Geren said. "I can't say enough about what he did."
Duchscherer will fly back to Oakland to have his right hip examined. He had season-ending surgery on the same hip midway through last season and said he first felt discomfort during his last start.
"I felt that if I kept pushing off, I'd make it worse," said Duchscherer, who represented the A's in this year's All-Star Game.
Mark Ellis homered and Kurt Suzuki had two RBIs for Oakland, which got a nice effort from Saarloos after he was called up from Triple-A Sacramento earlier in the day to bolster a struggling A's bullpen that was 1-5 over its last 18 games.
Oakland is 6-23 since the All-Star break and blowing a three-run lead to Minnesota after its ace left with an injury could've made a bad second half even worse.
"We're going to have the opportunity to be spoilers," Ellis said. "We need to get back to playing how we played the first month and start scoring some runs. It was nice to get out early tonight."
Saarloos (1-0) wants to be a starter, but is happy to be back in the majors for now. This is Saarloos' second stint with the A's this season. He last pitched in the majors on April 17.
"I see myself as a starter, but this is what I am here for," he said. "You just have to be ready."
A's right-hander Brad Ziegler surrendered an RBI triple to Joe Mauer in his first outing since his career opening scoreless streak of 39 innings was snapped on Thursday against Tampa Bay. Ziegler tied a 59-year-old major league record for relievers with his streak.
Mauer scored when left fielder Eric Patterson's throw skipped into Minnesota's dugout, cutting Oakland's lead to 3-2. Justin Morneau followed with a single but Ziegler got Jason Kubel to ground into an inning-ending double play.
Ziegler also worked the ninth for his third save in as many chances.
"The damage was done early and they held on," Twins manager Ron Gardenhire said.
Saarloos, a 29-year-old who has spent time with Houston, Cincinnati and Oakland, retired 11 of the 13 batters he faced, baffling a Minnesota team that now trails the White Sox by one game in the AL Central. Chicago beat Seattle 13-5 on Monday.
"We feel pretty good with ourselves. We're not going to quit and we got back into it," Gardenhire said. "With our ballclub you feel like you're going to find a way to get a big hit and tie the ballgame. We just couldn't come up with one."
The Twins didn't get a runner past second base until Kubel reached third on Randy Ruiz's two-out double in the seventh. Huston Street then got Brendan Harris to line out to shortstop to end the threat.
Ellis went deep on Nick Blackburn's first pitch for his third career leadoff homer and first since Aug. 25, 2005, against Detroit. It was the second straight game Blackburn gave up a leadoff homer.
"That's frustrating. I think I'm going to have to be more dialed in when I come into the game," he said. "I can't be starting a game off like that."
The loss snapped a four-game winning streak for Minnesota and wasted a good start from Blackburn (9-7).
The rookie pitched eight innings, allowing six hits and three runs.
Twins 2B Alexi Casilla began a rehab assignment with Class A Beloit on Monday. If all goes well, he could be activated by Wednesday. ... Saarloos, who was 9-4 with a 4.22 ERA for Sacramento, replaces Dan Meyer in the A's bullpen. ... Gardenhire didn't start CF Carlos Gomez for the second day in a row. Gomez leads the team with 112 strikeouts and his on-base percentage has dropped to .286. "I want him to think about those things, and continue to work hard. He'll be fine. He's game on, no matter what we do," Gardenhire said. Gomez pinch ran in the ninth. ... Oakland's game on Sept. 7 against Baltimore has been moved to Sept. 6 as part of a day/night doubleheader. ... Twins SS Adam Everett left the game in the sixth after getting hit on the hand in the dugout by a Nick Punto foul ball. X-rays were negative and he should be available Tuesday.