McCardell (1-2) allowed one hit over six innings for his first win and Mauer knocked in a pair of runs in the first game of his rehab assignment as the Fort Myers Miracle edged the Jupiter Hammerheads, 3-1.
"It was pretty sweet," McCardell, who turned 24 last week, said of working with Mauer. "We knew he was coming, I found out yesterday, so it was pretty awesome to throw to a Major League catcher, to an All-Star-caliber catcher, somebody like him who knows his stuff as well as he does."
McCardell was excited for the opportunity, especially after giving up six runs in his previous start on Sunday. Mauer, on the disabled list with back pain, went 2-for-4 and drove in two runs to further help his starter.
"He's a great guy," McCardell said. "And I felt real good out there. The last two starts were pretty below-average, so I've been working on stuff with my pitching coach, Steve Mintz. My consistency felt a lot better tonight, I was mixing up my pitches and getting ahead."
McCardell, the Twins' sixth-round pick in 2007 First-Year Player Draft, held the Hammerheads to a leadoff single by Geraldo Valentin in the opening inning. He walked one and hit a pair of batters.
"I was able to get into better counts, which helps," said McCardell. "I was throwing a good two-seamer into righties and four-seamer into lefties, a good change and curve that got better as the game went on."
Mauer's two-out double in the third plated Estarlin De Los Santos to give the Miracle a 1-0 lead. Chris Parmelee singled home De Los Santos again in the fifth before Mauer struck again two innings later with an RBI single.
McCardell said he and Mauer talked things over before the game.
"I have a lot of confidence and he knows what he's doing," the Pennsylvania native said. "We had the same plan the whole night, to pitch to different sides of the plate. I wasn't really nervous."
Neither was Mauer, who is scheduled to get about 50 at-bats with Fort Myers, ideally with at least half of those coming as a catcher. If all goes well, the Twins hope he can return to the Majors by early May.
McCardell has a slightly longer route if he intends to reach Minnesota.
"A lot of it is out of your hands, so you stay positive and keep trying to get better, keep improving and get your game as high as you can get it," said McCardell, who went 9-4 with a 2.86 ERA in 22 appearances, including 21 starts, for Class A Beloit last year. He ranked fourth in the Midwest League with 139 strikeouts.
"You can't control it, so every fifth day I just go out and work on stuff," he said.
Danny Wild is an editor for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.