The Oakland Athletics scored six runs off him that inning and two more off reliever Bruce Chen, giving them an 8-0 lead and sending them on their way to a 16-4 victory over the Rangers at Rangers Ballpark in Arlington on Friday.
The Rangers have now lost three straight and six of their last eight games.
"We certainly didn't get much out of our pitching tonight," manager Ron Washington said. "I told my guys to take a shower and let this one go down the drain. There's still a long season left. We've just got to keep fighting and get this thing turned around."
McCarthy was the starter in two of those six losses, pitching a total of three innings while allowing 12 runs on 10 hits, three walks and a hit batter. He is now 1-3 with a 10.20 ERA after four starts.
"It's not fun to do this and be 1-3," McCarthy said. "I expect a lot better of myself than this. I'm trying to stay positive because every time you struggle, you can learn something. To me, I have to be better mechanically."
He faced just 10 batters on Friday and allowed seven to reach base on four hits, two walks and a hit batter. He walked Shannon Stewart in the top of the first, then got Nick Swisher and Eric Chavez to fly out, and Mike Piazza to strike out.
But Piazza was the last batter he retired.
Milton Bradley started the second with a single, Travis Buck worked a walk, and Bobby Crosby lined a double to left to give the Athletics a 2-0 lead. McCarthy then hit Jason Kendall. Mark Ellis doubled to center to score one run and Stewart singled to center to score another run.
That made it 4-0 and still left the Athletics with runners at the corners with nobody out.
"This one was different from the last one," said McCarthy, who gave up six runs in two innings against Seattle last Sunday. "This one, I was just screwed up mechanically.
"It was bad mechanics. I lost focus there. I'm concerned from the point of view that the mechanical flaws are not ruining an inning for us but ruining the game."
Added Washington: "It's just some adversity he's going through. He's got a good head on his shoulders. He has some things to learn, but before it's over, he'll figure it out. We'll give him a chance to figure it out. He just has to get the ball down in the zone and hit his spots. If you don't hit your spots, they'll hit them for you."
Washington tried to go to his bullpen to salvage the inning, but that did little good. Not even the Rangers relievers, who had been quite good for much of the month, could get away from this one unscathed.
Four more came across after Bruce Chen took over as Travis Buck put the finishing touches on the inning with a three-run double. Chen allowed two inherited runners to score, the first two inherited runners that a Rangers reliever has allowed to score this season.
Buck also had a two-run home run off Chen in the fourth, and the Athletics pounded Joaquin Benoit for six runs in the eighth. The Rangers bullpen ERA went from 3.43 to 4.97 in one night, and Benoit, who had been pitching so brilliantly since the beginning of Spring Training, saw his ERA skyrocket from 3.18 to 10.80.
The Rangers used six pitchers on the night and they combined to throw 222 pitches. The loss also left them 1-6 in their division.
"It's not good," Washington said. "But you can also go on a winning streak, which we are capable of doing. Nothing is lost right now. It's a matter of getting it turned around and hitting on all cylinders. We'll do that."