TORONTO — Lucas Giolito and the Red Sox were cruising, up 6-0 with two outs in the bottom of the sixth inning and nobody on base.

That’s when things began to take a turn. Boston blew its six-run lead and lost 7-6 in 10 innings to the Blue Jays here at Rogers Centre.

“Gotta finish stronger,” Giolito said. “Sucks to give the other team momentum like that when you’re up big.”

Giolito pitched well in his Red Sox debut, 17 months after signing a two-year, $38.5 million contract. The 30-year-old righty allowed three runs, five hits and two walks while striking out seven in 6 innings

“I thought I pitched well until the sixth,” Giolito said. “Sixth inning, some crucial, crucial mistakes. 0-2 walk. 0-2 homer. Another homer.”

Manager Alex Cora agreed that the game began to take a turn when Giolito walked George Springer with two outs after being ahead 0-2 in the count. Springer worked a seven-pitch walk. He fouled off a pitch and took four balls, including a borderline pitch that was close to the top edge of the strike zone that was called ball four.

“If Gio throws the ball like that the whole season, we’re going to be in good shape,” Cora said. “But I think the walk changed the whole game.”

Daulton Varsho followed up the walk by a 0-2 changeup from Giolito that caught too much of the plate for a two-run home run. Alejandro Kirk then homered on a changeup Giolito left right down the middle of the plate.

He induced four swings-and-misses with this changeup, his best secondary pitch.

“We were playing the changeup pretty well to the corners and I just left them up there,” Giolito said. “So something to learn from.”

Giolito was at just 72 pitches with two outs in the sixth before walking Springer. Cora said it wasn’t difficult deciding whether to let him keep pitching into the sixth inning after he had been so efficient through five innings.

“Not at all,” Cora said. “He was built up to go 90, 95 pitches. And like I said a few weeks ago, we’re gonna let them go. And he did an outstanding job.”

Cora said Giolito had a good fastball and changeup. Giolito got five swings-and-misses with the fastball. He topped out at 96 mph with it when he struck out Vladimir Guerrero Jr. swinging to pitch out of a jam in the third inning.

“Obviously he’s upset with the way it ended, but I think if we get this version of Lucas, we’re going to be in good shape,” Cora said.

Giolito added, “The biggest takeaway from tonight is stay focused and finish strong.”

Garrett Whitlock made a crucial mistake when he left a 2-0 changeup up in the strike zone to Anthony Santander in the seventh inning with two runners on base. Santander blasted it 398 feet for a three-run home run that tied it 6-6.

“That’s frustrating. Never want to do that,” Whitlock said.

Whitlock was trying to throw the pitch to the outside edge of the zone.

“Yeah, it was an unexecuted pitch … and it went out,” Whitlock said.

Giolito spent last year on the 60-day IL after an internal brace procedure to repair his damaged right elbow. He began this season on the 15-day IL with a left hamstring strain.

“The first five innings we kind of saw the slider wasn’t really there,” Giolito said. “Another thing, (catcher Carlos Narváez) was fantastic behind the plate. Couldn’t ask for a better catcher back there for my first one back in a long time. He was seeing everything. We were able to work the heater down and up … Also commanding the changeup to the corners, keeping it down. And so the sixth inning, just left a couple crucial ones up in the zone and they were able to get good swings off.”

Boston’s top three hitters, Jarren Duran, Rafael Devers and Alex Bregman, combined for five hits. The rest of the lineup had just two.

“We didn’t do much offensively,” Cora said. “I think there was one base runner from the sixth inning on. We didn’t put too much pressure on them. So yeah, we’ve got to finish games. That’s part of it.”