Sox lose to A's, 7-3, their 38th setback in the last 54 games in Oakland.

OAKLAND, Calif. -- Mookie Betts lodged a rare argument of a called third strike. Alex Cora ventured out of the dugout, risking his first ejection of the young season. Andrew Benintendi went down looking and slammed his helmet without leaving the batter’s box.

All of this happened within a six-pitch span in the top of the sixth inning Thursday afternoon. The Red Sox were on their way to a second defeat in as many four-game series this season, their frustrations threatening to boil over.

Not that the Athletics seemed to mind all that much. Oakland extended its mastery of Boston at this venue thanks to a 7-3 victory.

Stephen Piscotty’s three-run homer in the bottom of the third erased a 3-0 deficit and the Athletics were off and running at Oakland Coliseum. Robbie Grossman’s RBI double and a bizarre ground-rule double by Piscotty accounted for three more runs in the fourth, chasing Boston starter Eduardo Rodriguez. The Red Sox find themselves limping toward Arizona to close out what has been a difficult season-opening road swing.

“We didn’t play well in Seattle,” manager Cora said. “We didn’t play well here. Now we go to Arizona, it’s a three-game series and we have to play better. That’s the bottom line.”

Rodriguez was relatively sharp early before hitting the wall in the third. Josh Phegley’s double to left and Marcus Semien’s walk set the stage for Piscotty, who lifted a towering drive to center that cleared the wall at the 400-foot mark. It was a brand new game at 3-3 and the 14th home run allowed by Boston’s starting rotation to date.

“If you fall behind in the count that’s what happens all the time,” Rodriguez said. “I tried to throw a fastball away and I missed it right down the middle of the plate.”

More trouble followed in the fourth. Grossman sent a liner to the corner in right to break the tie and Piscotty followed one batter later with a lazy fly to right center. Betts and Jackie Bradley Jr. failed to communicate and the ball hit on the warning track, bouncing high over the wall for a ground-rule double that made it 6-3.

“One of us should have caught it,” Betts said. “It was one of those things where it was right dead in the middle. One of us should have talked for sure.”

“In the moment I’m thinking the ball has to be caught regardless of who it is,” Bradley said. “It doesn’t really matter. I have to make that play.”

Khris Davis added the extra point with an RBI single to center in the sixth, but by then the game was well out of reach. Oakland’s bullpen combined for four strikeouts and conceded just a pair of singles. It was the 38th victory for the Athletics over the Red Sox in their last 54 meetings here.

“Right now we’re not paying attention to details,” Cora said. “That’s on us. That’s on me. That’s on the staff.”

Starter Brett Anderson was on the brink early for Oakland, as the left-hander’s home scoreless string of 34-1/3 innings didn’t last through the first. Xander Bogaerts and Brock Holt each drew a bases-loaded walk to make it 2-0 in the first, but Christian Vazquez grounded into a fielder’s choice to stop the rally.

J.D. Martinez drilled a solo homer to right in the third and Boston nearly produced an immediate answer in the fourth. The Red Sox loaded the bases with two outs before Anderson struck out Steve Pearce on a breaking ball down in the zone. Boston put just one more runner in scoring position over the last five innings.

“We’re playing against some teams that are really executing, and that’s not what we are doing,” Bradley said. “We have to execute better and play a lot better.”

The final indignity came in the ninth, a second curious play of the afternoon involving Betts. He drew a leadoff walk and attempted to reach third on a single to shallow center by Benintendi. Ramon Laureano recorded his third outfield assist of the series for the Athletics by throwing Betts out on the run.

“I should have known,” Betts said. “He’s pretty much thrown everybody out. That’s what my instincts told me to do and I should have let myself know before anything even happened that my run meant nothing.”

“Three plays were bang-bang plays, but that one right there can’t happen,” Cora said. “And (Betts) knows it. He came up to me. For how great a player he is, he makes mistakes. And he owned it.”