McCarthy and Matsuyama share lead at St Jude's Championship
Despite struggling with a hip injury, McCarthy posted a fine 7-under round of 63 while Matsuyama shot 64 to head into the weekend on top of the leaderboard.
The 31-year-old McCarthy, who has yet to win on the PGA Tour but suffered playoff defeats this year and last, got off to a fine start with four birdies in his opening six holes before a bogey on the par-4 seventh.
He recovered with a birdie on the par-3 eighth and showed the same resilience when he bogeyed the 12th and immediately birdied on the next hole.
"It was a really good round. I did everything pretty well. I putted well. I hit a lot of good iron shots. Bounced back nicely after a couple of the bogeys I had. Everything felt really solid today," he said.
McCarthy's performance was even more impressive given the hip trouble he has been coping with.
"I don't want to divulge too much. It's bothering me, and I've been able to do enough the last few days to push through it," he said.
"The heat really helps it. It really loosens it up. But I've had to spend a lot of time post-round, pre-round getting it loose, getting it ready to go to play a full round."
Matsuyama started with a birdie on the par-4 first hole but then missed a short birdie putt on the second and he bogeyed the par-3 fourth after driving into the water.
From then on though, the 2021 Masters champion was in control, bogey-free and making five more birdies.
Matsuyama is looking for his 10th win on the PGA Tour and his second of this season following his victory at the Genesis Invitational in Los Angeles in February.
American Sam Burns was a stroke behind the leading pair after carding a 63 with an eagle on the par-5 third hole.
Scottie Scheffler, fresh off his Olympic gold medal in Paris, leads the FedEx Cup playoff standings and is in contention yet again with his solid bogey-free 65 putting him on nine-under, two off the leaders.
"I did a good job of having some nice up-and-downs to kind of keep the momentum and the round going. I holed a nice putt for par early in the round on 5 and then I had a couple nice chips after that getting it close to the hole making what could have been a stressful par into a pretty stress-free par with some nice pitches. Overall it was a pretty good day," said the reigning Masters champion.
England's Justin Rose was a stroke behind Scheffler after a second straight round of 66.
Rose ended his round in style with birdies on the 16th and 17th and he sits level in fifth place with American Nick Dunlap.
It was a disappointing day for Rory McIlroy, fifth in the FedEx Cup standings, who shot a three-over 73 after making a double bogey on the par-5 third where he drove into the water.