SAN FRANCISCO – Monday night was a microcosm of what has been a confounding season for veteran Alex Cobb. 

Cobb was charged with six runs over six innings as the Giants dropped their fifth in a row with a 13-3 series-opening loss to the Mets at Oracle Park, though the 34-year-old right-hander once again pitched better than his final line indicated.

• Box score

A defensive miscue opened the door for the Mets to score five runs with two outs in the third inning, extending Cobb’s stretch of misfortune on the mound.

Cobb now has a 6.25 ERA through seven starts for the Giants, but his peripherals suggest he’s been the unluckiest pitcher in baseball this year. The gap between his ERA and his expected ERA (1.90) is the largest among pitchers who have thrown at least 20 innings this season, with his expected batting average (.195) and expected slugging percentage (.277) showing that he’s limiting hard contact without much to show for it, thus far.

“It’s tough,” Cobb said. “You put so much into each pitch. You execute the pitch. You induce weak contact and they get rewarded for it. … I try not to get too frustrated. I try to keep that inside, but there were a couple tonight that I would have liked to be outs.”

Not much seems to be going right for the Giants (22-19), who have been outscored 38-15 over their second five-game skid of the month and are attempting to weather another rash of injuries after losing four players -- LaMonte Wade Jr., Curt Casali, Brandon Belt and Austin Slater -- to the injured list in the last four days. They sent outfielder Luis González to the mound for the second consecutive game as they slid a season-high six games behind the first-place Dodgers in the loaded National League West.

Cobb struck out the side in the first inning and seemed to be cruising early, but his outing went sideways when the Mets turned a string of soft contact into a five-run rally in the third. With a runner on first and two outs, Cobb gave up back-to-back infield singles to Brandon Nimmo and Starling Marte that loaded the bases for Francisco Lindor.

Lindor then sent a flare to left field that had an expected batting average of .010, but Darin Ruf couldn’t make the play, tumbling hard into the protective netting down the left-field line and allowing the ball to fall for a ground-rule double that knocked in a pair of runs to tie the game, 2-2.

“He gave us everything he had,” manager Gabe Kapler said of Ruf. “He wasn’t able to catch the baseball. He’s the type of guy who’s going to make a big difference with his offense. When he’s at his best, he makes a lot of plays on defense, as well.”

Pete Alonso followed with the dagger, crushing a first-pitch knuckle curve from Cobb out to right-center field for a three-run shot that put the Mets ahead for good.

“That’s why I feel horrible that I didn't make that play for him,” Ruf said. “He’s been excellent. If I make that catch, he’s out of that inning with no runs instead of giving up five. He’s got great stuff. It seems like a lot of times the hits that they’re getting are infield singles and then there’s just maybe one big swing in the game where the infield singles happen to come right before that. He’s been excellent for us. The numbers don’t really tell how well he’s done for us.”

Cobb worked around another pair of infield singles to post a scoreless fourth and fifth, but he surrendered a two-out RBI double to J.D. Davis that stretched the Mets’ lead to 6-2 in the sixth. Cobb exited after allowing 10 hits -- four of which didn’t leave the infield -- and striking out seven in the 90-pitch outing.

“I thought Alex came out with good stuff,” Kapler said. “I know that he’s one of the best competitors on our team and deserves better with the stuff that he’s coming out with. I think he’s got the capability to pitch deep into games for us with the score on our side. It’s just not happening for him right now.”

Still, there are reasons to believe that Cobb’s luck will eventually turn. He’s throwing harder than ever, with his sinker topping out at 96.6 mph on Monday, the highest mark of his career. He’s also averaging 89.4 mph on his splitter, up from 87.5 mph in 2021. Overall, he’s racked up 39 strikeouts and issued nine walks over 31 2/3 innings while allowing only three homers.

“He’s as tough as they come mentally, so he understands that there are some challenges right now,” Kapler said. “We’re not making as many plays as we can. Sometimes there are balls that are just finding grass and not gloves. That can be really frustrating for a starting pitcher who’s as competitive and prepared as Alex is.”