Hardy broke a 1-all tie in the fifth inning with a line drive home run off Carl Pavano (6-10) that sailed over the left-field wall. Mauer, the Twins first baseman, had a play on a foul pop earlier in the at-bat, but couldn't make the catch when a fan wearing a Mauer jersey in the front row appeared to get in his way.
"Someone was saying he had a Hardy jersey on," the Baltimore shortstop said with a grin. "Any time you get a second chance, it's nice."
Twins manager Ron Gardenhire, ejected in the eighth along with third baseman Danny Valencia, was quick to defend the fan after the game.
"You can't blame our fans for reaching up and trying to catch the ball," he said. "You can boo them, like I heard, but that ball's in the stands. That's not why we lost the game."
Kevin Gregg pitched the ninth for his 18th save.
One of the few highlights for Minnesota was a spectacular catch by Ben Revere.
The center fielder sprinted toward the wall after Vladimir Guerrero hit a ball to the deepest part of Target Field in the top of the seventh. As both feet hit the wall, Revere reached up with his glove, caught the ball and tumbled to the ground.
"I looked in to make sure it didn't come out," Revere said. "I was sort of like, I did! It didn't come out! Wow!"
Britton (7-9) was activated from the disabled list before the game and made his first start since Aug. 4. The 23-year-old lefty allowed one run and six hits over five innings.
"It's good to get a win, but we needed it as a team," Britton said. "To come out and get the win on the first day here, it sets the tone for the next three games."
Britton walked four and threw 98 pitches, but managed to get the best of Twins designated hitter Jim Thome, the newest member of baseball's 600-home run club.
Thome failed to drive in a run with the bases loaded twice, flying out to left in the third and watching Britton's fastball catch the outside corner for strike three in the fifth.
"It was big," Britton said. "Any time you can get out of those situations, especially in a close game and especially on my first game back, to be able to get out of there where I haven't been able to in the past was pretty big."
One day after getting shut out by the Yankees, Minnesota managed just a single run on Mauer's groundout in the third and lost for the 16th time in 21 games.
The Twins could use Hardy's bat, but they traded the shortstop to Baltimore in the offseason for Jim Hoey and Brett Jacobson. Minnesota also was concerned about Hardy's oft-injured wrist.
The wrist has been fine and Hardy has 24 homers and 60 RBIs, while Hoey posted a 7.71 ERA in 17 games with the Twins early in the season and Jacobson remains in the minors.
Hardy did not have any extra bounce in his step while rounding the bases, and he refused to say anything negative about the Twins after the game.
"It's all the same. It's not like I'm going out there trying harder to try and prove a point," Hardy said. "It's just another game for me."
Pavano pitched seven innings, allowing four runs and nine hits.
Orioles manager Buck Showalter talked after the game about the need for his starters to be more efficient with their pitches. But reliever Michael Gonzalez has had no problems being efficient lately.
When Britton was removed, Baltimore's bullpen kept the Twins off the scoreboard.
Gonzalez fanned Jason Kubel with runners on second and third and two outs in the seventh, then struck out the side in the eighth. The left-hander threw 14 of his 24 pitches for strikes.
"He's been pitching well for a while now," said Showalter, whose team has not won a series since June 24-26 against Cincinnati. "He's attacking the zone. He's pitching with a purpose and he's got a good look in his eye."
Gardenhire has been ejected 60 times in his career. ... The Orioles put reliever Jason Berken on the 15-day DL with a right shoulder strain and optioned INF Blake Davis to Norfolk. ... Showalter said he expects Jeremy Guthrie to start on Wednesday and Jo Jo Reyes on Thursday. ... Adams batted .303 in 39 games with Norfolk before being recalled. ... The Aug. 14 postponed game between the Indians and Twins has been rescheduled for 1:05 p.m. EST on Sept. 24, creating a day-night doubleheader. ... Thome was selected AL player of the week. He slugged his 600th career home run on Aug. 15 in Chicago. ... Brian Duensing starts the second game of this four-game series for the Twins on Tuesday. Duensing has lost his last four starts. ... Alfredo Simon will make his first career start against the Twins on Tuesday. He has two saves and has not allowed a run in 4 2/3 innings of relief against Minnesota.