McCarthy matched a career high with 10 strikeouts after missing his last start with a sore right shoulder, leading the hobbled but surprisingly sharp A's past the Detroit Tigers 3-1 on Saturday night.
The A's, who added cleanup hitter Yoenis Cespedes to the disabled list earlier in the afternoon, have won seven of 10 to improve to 18-16 this season.
"There's a lot more talent here than I think there has been in the last few years," McCarthy said. "There are some guys who are coming through and filling in that are doing a really good job of it. We've got a better mental attitude this year. We're much more of a team unit, we have a lot more fun and I think it's just easier for everybody to fill in.
"You're expecting success as opposed to kind of fearing failure."
The A's Opening Day starter allowed four hits in seven innings to quiet fears of another serious injury setback. McCarthy (3-3) had struck out 10 batters only twice before.
"I think it's just terrific," A's manager Bob Melvin said. "Good teams don't let injuries get them down or use them as excuses."
Doug Fister's scoreless streak ended at 11 innings when Gomes grounded a single to left field in the first. Fister (0-1) struck out eight in six innings, allowing five hits and one run.
Detroit (16-17) has dropped four of six to start its nine-game road trip and is below .500 for the first time all year.
"You can look better swinging the bats and still not get any hits. I've seen signs but not many," Tigers manager Jim Leyland said. "We're just not looking good swinging the bats. We're not putting anything together."
Delmon Young doubled off Brian Fuentes with one out in the ninth and scored on Alex Avila's fly out. Fuentes, who earned his closer role back for now, earned his second save in three chances this season.
Relief is exactly what Oakland needed after a day filled with injuries.
The A's placed Cespedes on the 15-day disabled list with a strained muscle in his left hand. First baseman Kila Ka'aihue also was a late scratch from the lineup after he strained a hamstring sliding into second Friday night, and second baseman Jemile Weeks sprained his left ankle running out a single in the second.
Pennington replaced Weeks in the fourth. He played shortstop and Eric Sogard moved to second. Ka'aihue and Weeks are day to day and could be back in the lineup Sunday.
The player with the most injury questions entering the weekend ended up answering every one of them.
McCarthy controlled his pitches with ease and seemed to only grow stronger in the later innings. He struck out the heart of Detroit's lineup swinging in the sixth -- including Miguel Cabrera, Prince Fielder and Young -- and never put himself in a jam.
The only time the Tigers even threatened to score came in the fifth, when first baseman Barton let a popped bunt by Danny Worth drop -- perhaps thinking he had a chance for a double play -- only to watch the ball spin backward and foul. After Worth sacrificed two runners over, McCarthy rallied by striking out Don Kelly and inducing a groundout from Andy Dirks.
It was the third time in McCarthy's career that he struck out 10. The last time came in a 3-0 victory over the Seattle Mariners on Sept. 3, when McCarthy tossed a three-hitter.
"It's not a thought in my mind anymore," McCarthy said of his shoulder. "When Prince Fielder and Miguel Cabrera are there, worrying about yourself is pretty counterproductive."
Oakland RHP Brett Anderson is scheduled to throw about 40 pitches in a bullpen session on Monday in another step forward from elbow-ligament replacement surgery last July. ... CF Austin Jackson entered in the eighth, striking out against Cook. ... The Tigers send reigning AL MVP and Cy Young Award winner Justin Verlander (3-1, 2.63 ERA) to the mound opposite Jarrod Parker (1-0, 1.80 ERA) in Sunday's series finale.