Life also has been good for the White Sox, who have been stubbornly holding off the Tigers from their first-place perch in the American League Central.
Right-hander Gavin Floyd, McCarthy's mound opponent on Friday, has done his part to help the White Sox cause, but he's coming off a performance in which he allowed five runs in 6 1/3 innings.
McCarthy, who made it through a 23-pitch bullpen session on Wednesday with no problem, will be making his first start in the Majors since June 19 after being sidelined by the same right shoulder soreness that has plagued much of his career.
Before he was sidelined, McCarthy was having a terrific season, compiling a 6-3 record with a 2.54 ERA in 12 starts.
He was the A's Opening Day starter and completed at least six innings in all but two of those outings. He made it through seven innings in seven of those starts.
McCarthy's loss was a blow to the A's, but they've done just fine in his absence, going 27-15 and surging into second place in the American League West.
Their 9-8 victory over the Angels on Wednesday gave them two straight victories in the series after losing the opener. It also left them 5 1/2 games behind the first-place Rangers.
"He's very efficient with his pitches," A's pitching coach Curt Young said of McCarthy after Wednesday's bullpen session.
"That's the key to his game. He gets a lot of early outs and makes things happen quick."
McCarthy made two rehab starts with Triple-A Sacramento, the most recent on Sunday, when he pitched six shutout innings while striking out nine and giving up two hits.
Floyd has been solid for the White Sox, who lead the AL Central by one-half game over the Tigers, but in his last start on Saturday against the Angels, he had a tough time getting off the mark in the first inning, throwing 40 pitches and surrendering three runs.
Floyd hit leadoff hitter Mike Trout with a 1-2 pitch then walked three straight to force home a run and gave up two hits.
"When it's happening like that, you just keep telling yourself one pitch at a time, you can easy get out of this," Floyd said. "I found a groove eventually but obviously it'd be nice to do it from the beginning."
Floyd did pull himself together and wound up pitching 6 1/3 innings to save the White Sox bullpen, something his teammates appreciated.
"I give him credit because he saved our bullpen by giving us 6 1/3 innings," catcher A. J. Pierzynski said. "It got really ugly, but he battled and fought. Something I told him he should be proud of, because while it wasn't his best start, he saved everyone else on the team by going as deep as he did and giving us the innings he gave us."
A's: Kottaras hits first homer
Catcher George Kottaras hit his first home run as a member of the A's in Wednesday's victory over the Angels.
Kottaras came to the A's from Milwaukee on July 27 in a trade for pitcher Fautino de los Santos.
White Sox: Pierzynski, Rios hot
A.J. Pierzynski (.371, 13-for-35) extended his hitting streak to 10 games in Wednesday's 2-1 loss to the Royals. Pierzynski was 2-for-4 in the game.
Alex Rios (.395, 15-for-38), who owns a nine-game hitting streak, did not play in Wednesday's game.
The A's are hoping McCarthy can throw 80-90 pitches on Friday as he takes the rotation spot of the injured A.J. Griffin, who had to leave his last start Saturday against the Blue Jays with shoulder tightness after pitching to two batters in the second inning.