SAN DIEGO — Red Sox starter Lucas Giolito walked four straight hitters, including forcing in the game-tying and go-ahead runs during a difficult fifth inning.

“I know that the way baseball works, the L doesn’t go next to my name but it should,” Giolito said. “That was really bad.”

The Red Sox lost 5-4 to the Padres in 10 innings at Petco Park.

Roman Anthony tied it 4-4 in the ninth inning with an opposite field RBI double. But despite the star rookie’s heroics, Boston couldn’t capitalize in extra innings.

David Hamilton struck out on a fouled off bunt attempt during Boston’s scoreless top of the 10th inning. The Padres then walked it off on the first pitch from reliever Garrett Whitlock in the bottom half. Ramón Laureano connected on a slider from Whitlock for a game-winning single.

“I lost feel,” Giolito explained. “I felt a little uncomfortable all day, but we were battling and pitching OK. In the fifth inning, I lost feel for my mechanics and I just couldn’t make the adjustment.”

Giolito gave up a fifth-inning leadoff single to Fernando Tatis Jr. before retiring Luis Arráez on a groundout and Manny Machado on a fly-out.

He then walked four straight batters for the first time in his career.

“It’s inexcusable,” he said. “I truly believe that if I had just gotten out of that fifth inning, made the adjustment, then we would have won that game. Chappy (Aroldis Chapman) would have been pitching for a save instead of in a tie-game situation.”

Manager Alex Cora added, “We were one pitch away, one out away from getting out of the inning. We’ve got to trust these guys to give us 100 (pitches), at least five innings. It just didn’t work out.”

Cora pointed out that Xander Bogaerts walked during the fifth on a pitch that landed in the strike zone.

“There was a pitch there to Xander, the 3-1 that we thought it was in the box,” Cora said. “But when you’re all over the place, then you know you’re not gonna get calls. That’s how it is. So we’ll make adjustments and he’ll be ready for Miami.”

Giolito dismissed the idea he was having trouble with the mound and his landing spot.

“I didn’t have any issues with the mound at all,” he said. “I got uncomfortable there and I wasn’t able to make the adjustment. So we’ll dive deeper into it and see. I don’t know if I was rushing over-striding. But yeah, I just lost the ability to throw strikes and can’t happen at this level.”

Giolito threw his four-seam fastball 49% of the time, followed by 31% sliders.

“I was riding it (the fastball) pretty good,” he said. “I was happy with how it was playing, but lost feel for it. I mean, I couldn’t really land a slider either.”

Giolito walked Ryan O’Hearn on a 3-1 fastball to force in the game-tying run. He walked Laureano on a 3-2 fastball, giving San Diego a 4-3 lead.

“It’s terrible because I’m thinking (about) the implications of the game,” Giolito said. “We have a lead. Pitching well enough to protect that lead. If I get out of that inning sooner, maybe I get six (innings). If I get out of it at some point, it’s five (innings). We exit with the lead. I have so much confidence in our bullpen. They’re just amazing. So I know they would have done their job like they did after they had to come in and bail me out. It’s a game we could have won if I had just made that adjustment.”