The only problem from the Rangers' standpoint is that he's doing it for the A's, and McCarthy will be facing them on Thursday afternoon when the two teams wrap up a two-game series at Rangers Ballpark in Arlington.
The Rangers thought McCarthy would be a front-line pitcher, but he was on the disabled list five times in four years.
Ultimately, Texas put him on outright assignment after the 2010 season, but he refused and signed with Oakland.
McCarthy has compiled a 3-3 record with a 2.56 ERA in eight starts for Oakland this season.
In his last outing Saturday, in a 3-1 win over the Tigers, McCarthy pitched seven innings, giving up four hits and striking out 10 while throwing 91 pitches.
Rangers general manager Jon Daniels said it's gratifying to know that McCarthy seems to be the pitcher the team felt he'd become when they acquired him.
"At one point, we were really high on him," Daniels said Wednesday. "He just couldn't stay healthy. To his credit, he's put the work in and turned that corner.
"In some ways, it's good to see from an evaluation standpoint that he was capable of pitching at a big league level like we had hoped. Unfortunately, it didn't happen here."
McCarthy is happy being with the A's.
"There's a lot more talent here than I think there has been in the last few years," he 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 fit in.
"You're expecting success as opposed to kind of fearing failure."
A's: Inge may hit the DL
Oakland was hoping Brandon Inge would return for Thursday's game against the Rangers, but instead, he may land on the 15-day disabled list, retroactive to May 12.
The third baseman had missed four straight games with a sore right groin.
"From the beginning, I kind of downplayed it a little bit," Inge said Wednesday night. "It wasn't something I was trying to hide from them, but I really thought having dealt with this in Spring Training that I could cope with it and make it through it really quick."
After joining the A's when the Tigers cut him loose, Inge hit .227 with four home runs and 17 RBIs in 11 games with Oakland before getting hurt.
Rangers: Harrison hoping to get back on track
McCarthy will be opposed by left-hander Matt Harrison in Thursday's game.
Harrison is 4-3 with a 5.23 ERA in seven starts this season, and is 1-3 with an 8.66 ERA in his past four starts after winning his first three starts. He allowed four runs in six-plus innings in a 4-2 loss to the Angels on Saturday.
"Two-out walks ended up costing me," Harrison said. "My stuff is there. Sometimes I make mental mistakes, but my mechanics are good."
The Rangers' Josh Hamilton did not homer in Wednesday's game, but he had two hits in four at-bats to keep his average above .400 -- now at .404 -- while also extending his hitting streak to 16 games.