SAN DIEGO – Even as the Phillies enjoyed the thrill of perhaps their most unlikely victory of the season Wednesday afternoon, they still had to ponder the agony of another injury.

Reliever Seranthony Dominguez left with one out in the bottom of the eighth inning at Petco Park with what manager Gabe Kapler described as elbow soreness.

“He’s showing symptoms of a mild strain, but there is no current concern for the ligament,” Kapler said after the Phillies’ 7-5 come-from-behind win over the San Diego Padres. “He’ll have an MRI [Thursday] and we should know more at that point.”

Dominguez waved off reporters after the game. He has a 4.01 ERA in 27 appearances this season but is a vital reliever for the Phillies, who are already shorthanded in the bullpen.

Relievers Tommy Hunter (forearm strain), David Robertson (elbow soreness), Adam Morgan (forearm strain), Pat Neshek (shoulder strain), Edubray Ramos (biceps tendinitis), and Victor Arano (elbow surgery) are all on the injured list.

Arrieta shaky again

Jake Arrieta’s road trip got off to a shaky start Friday night when he allowed five runs on 10 hits, including three home runs, in a loss to the Dodgers. His start Wednesday against San Diego was just as bad, if not worse.

He allowed five more runs on seven hits, including two home runs. He has allowed 14 home runs for the season, which is tied for the second most in the National League. Colorado’s Kyle Freeland (16) is the only N.L. pitcher who has allowed more.

Arrieta also walked five batters. All five of the Padres’ runs scored after Arrieta had retired the first two batters of the inning.

With the Phillies ahead, 1-0, in the bottom of the third, Manny Machado reached base on a two-out double and Eric Hosmer walked to set up a three-run home run by rookie Josh Naylor on an 0-2 fastball at the top of the strike zone.

“I was just trying to go in,” said Arrieta, whose ERA is at a season high 4.29. “If you miss you have to miss off the plate. When you have a guy 0-2 and you throw a ball that’s hittable, they’re probably going to put a good swing on it.”

Will Myers followed Naylor’s home run by hitting an 0-1 curveball over the center-field wall to make it 4-1.

Arrieta’s afternoon ended with two outs in the fifth. He issued a two-out walk to Myers, who stole second and scored on a single to center field by Ty France, another Padres rookie. When Austin Allen, another rookie, walked, Kapler removed Arrieta.

“He didn’t have his best command,” Kapler said.

Extra bases

Vince Velasquez, in just his fifth relief appearance, retired all four batters he faced, including two via the strikeout, and picked up his second victory out of the bullpen … The Phillies will pay tribute to former team president David Montgomery on Thursday at Citizens Bank Park. The memorial ceremony is open to the public and will begin at 3:05 p.m. … Zach Eflin will return from the injured list to pitch the series opener Friday at home against Cincinnati.