McCarthy, who signed a four-year, $48-million free-agent contract with the Dodgers on Dec. 16, gave up an RBI double to Chris Dominguez in the second inning and three hits overall.
The right-hander, a projected starter, has allowed two runs on five hits in five innings, including two in his first spring start against the Brewers on March 8.
''It felt good, mostly to get in the work and then getting to where you know what you still have to work on,'' said McCarthy, who walked one and struck out one. ''There's still a lot to do. I've got to work my curve. But overall it's good.''
Jason Marquis, who is with his ninth team after signing a minor league contract with the Reds on Jan. 21, kept himself in the mix for a starting job in his third spring start. Marquis, 36, gave up one run on three hits in four innings.
''I always say I want to compete,'' said Marquis, who hasn't pitched in the major leagues since 2013 when he underwent Tommy John surgery while with San Diego. ''And I do compete every time I step on that mound, whether I've got a guaranteed contract or not.
''Like I said early on, I believe in myself,'' Marquis added.
Adrian Gonzalez had an RBI single off Marquis in the fourth.
Dodgers: Joel Peralta put in his first appearance, giving up a run on two hits in one inning. ''It just felt good to be out there,'' said Peralta, who was set back by stiffness in his right shoulder at the start of camp.'' I threw all my pitches. Did what I had to.''
Dodgers manager Don Mattingly was pleased with what he saw in Peralta, who the Dodgers acquired on Nov. 20 in a trade with Tampa Bay.
''Very much,'' Mattingly said. ''He looked sharp. We're not so worried about results right now. Just the process.''
Reds: Right-fielder Jay Bruce was a late scratch. Bruce has been nursing a strained right calf. Manager Bryan Price said he didn't want to risk further injury. Bruce has missed three straight games.
Dodgers: Left-hander J.P. Howell is expected to get in some work Saturday against Cleveland at Camelback Ranch. He has been troubled by some discomfort in his groin.
Reds: Right-hander Anthony DeSclafani gets his third spring start Saturday against Colorado in Goodyear. Over two innings against the Indians and three against the Angels, he's allowed four runs on seven hits and struck out two. DeSclafani, acquired on Dec. 11 in a trade with Miami, has put himself in the hunt for spot as the fourth or fifth starter.
Dodgers: Left-hander Brett Anderson gets his second spring start Saturday. In his first appearance, Anderson threw two scoreless innings Monday in a 5-5 tie with the Giants. Anderson, who signed a one-year, $10 million deal on Dec. 31, is coming off back surgery last August.