"They beat us today," Rangers manager Ron Washington said. "A grand slam home run ... a three-run home run. They swung the bats today."
McCarthy's start marked only the third time in 28 games that a Rangers starter failed to go five innings. They entered the game 6-1 with a 3.50 ERA in their last 12 games.
"It's amazing ... it stinks," McCarthy said. "The last time through the rotation, everybody did their thing. To come back to me and let it down is frustrating. This would have been a nice game to win. I just didn't get it done."
Oakland rookie starter Trevor Cahill made it through seven innings to get his first Major League victory. Cahill, 21, a second-round pick in the 2006 First-Year Player Draft, allowed five extra-base hits, including Chris Davis' seventh home run. He also allowed a pair of doubles to Marlon Byrd and Michael Young, but held the Rangers to 0-for-7 with runners in scoring position.
The Rangers' best chance to get an early lead came in the second inning when Byrd led off with a double into the left-fielder corner. But Cahill came back to strike out Nelson Cruz, get David Murphy on a grounder to first and strike out Davis to end the threat.
"We let him slip away," Byrd said. "First time facing a young guy ... he had different stuff, a knuckleball, a little slider, pretty good changeup. We need to make adjustments the next time we face him. If we give Brandon some runs early, things might have been different. He could have pitched more aggressively. Pitching has been keeping us in there, it's time for the offense to pick things up."
The Rangers were 0-for-10 with runners in scoring position until ninth-inning singles by Davis and Jarrod Saltalamacchia, and a double by Omar Vizquel. By then it was way too late.
McCarthy was pretty good in matching Cahill with three scoreless innings to start the game. Then he fell apart in the fourth. He gave up a leadoff single to Kurt Suzuki, and then walked both Jason Giambi and Matt Holliday.
"I made a bad pitch to Suzuki leading off the inning and after that I lost myself mechanically and the situation escalated," McCarthy said. "The walks are unacceptable. I have to go right after those guys. It started spiraling downward and I didn't adjust fast enough."
Instead Cust hit an 0-1 fastball deep over the right-field fence for a grand slam. Jack Hannahan's RBI double made it 5-0 before the inning was over and McCarthy was gone after giving up singles to Suzuki and Giambi to start the fifth. He is now 0-3 with a 16.87 ERA in his career against the Athletics.
"I felt like I started pulling off the ball," McCarthy said. "I got out of my rhythm and didn't make adjustments quickly."
Benson gave up a three-run home run to Holliday right away but was still able to give the Rangers three innings of work in his debut as the long man in the bullpen.
"I thought he did a great job," Washington said.