Ron Gardenhire was angry when he was ejected by umpire Bill Miller in the fourth inning Wednesday, but maybe he should have been happy. He didn’t have to witness the carnage that followed.

Oakland sent 13 batters to the plate in the inning, and became the first Twins opponent in more than five years to record a 10-run inning. Mike Pelfrey absorbed much of the punishment, but there was plenty of other damage for other pitchers in the 18-3 rout, the Twins’ worst loss of the season.

Minnesota already trailed 8-1 when Gardenhire was ejected for an unusual play that began as a foul ball. The A’s complained that the bases-loaded line drive off Jed Lowrie’s bat, which forced Miller to leap into the air to avoid being hit, had actually clipped the foul line as it landed behind him. The umpires conferred, and awarded Lowrie a double, sending two runners across the plate.

Gardenhire grew more irritated as he argued, and finally earned the 67th ejection of his career and fifth this season.

Pelfrey gave up seven earned runs, his worst outing as a Twin.

“You can’t fall behind in the count and throw the ball over the middle of the plate,” a downcast Pelfrey said after his record fell to 5-12 and his ERA rose to 5.31. “I put this team in a really bad spot, obviously. I fully take responsibility for this game. That’s terrible.”

Josh Roenicke allowed four of the fourth-inning runs, and Ryan Pressly the last two, on Stephen Vogt’s two-run homer. It was the worst inning the Twins had allowed since Aug. 4, 2008, when they blew a 6-0 lead and lost 11-6 at Seattle.

Eric Fryer was one of the few Twins to have a good night — he homered into the A’s bullpen in his first at-bat as a Twin. Merely cutting Minnesota’s deficit to 13 at the time “is not ideal, but they all count the same,” said the catcher and former Pirate. “I’ll remember it, but hopefully I forget the score. I’ll definitely remember the swing.”

Mauer has setback

Joe Mauer “didn’t have a good day” on Wednesday, General Manager Terry Ryan said, “so I didn’t have a good day.”

That’s because the Twins’ All-Star catcher felt some concussion symptoms return again after going through a workout, a setback as Mauer works toward a return from the Aug. 19 injury caused by a foul ball off his mask.

Mauer “didn’t have the response he was hoping for,” Ryan said. “I’m guessing that’s probably something that [Justin] Morneau went through many times during the course of” his own recovery from a concussion.

Mauer’s condition “is a concern,” Ryan admitted, “more than a frustration. You’ve got to feel for the guy. He just didn’t feel good today, so we sent him home. Hopefully he’ll come back tomorrow feeling better, and we’ll get back on track.”

The Twins had been optimistic that Mauer, who felt good enough to run the bases Monday with no aftereffects, might return during this homestand, but Wednesday’s setback makes that less likely. The Twins then depart on a weeklong road trip after Sunday’s game, and return Sept. 23 for the final week of the season.

One side effect of his injury, Gardenhire said, is irritability.

“Not only does he get irritated when you [media members] ask him how he’s doing, he gets irritated when I ask him how he’s doing,” the manager said. “So I just leave him alone, let him go about his business.”

Rookie homers revisited

An item in Wednesday’s Star Tribune correctly listed Jimmie Hall’s 33 home run season in 1963 as the franchise record for a rookie, but incorrectly listed those behind him. Tony Oliva’s 32 home runs in 1964 is second-most by a Twins rookie, and Gary Gaetti, who had 25 in 1982, is third.