TORONTO — It was a fitting end to a frustrating month.

The Yankees, who took a two-run lead into the bottom of the sixth inning on Monday night, completely unraveled in the frame as the Blue Jays scored four runs en route to a 5-4 victory in front of 40,619 at Rogers Centre.

The Yankees (48-36), who have lost 11 of their last 17, failed to build on their series win over the A’s this past weekend.

But the Blue Jays (46-38) are a far better outfit than the crew that visited the Stadium from Sacramento, showing why they came into the night with the third-best record (29-18) in the majors since May 8.

The Yankees, who entered June looking like one of the best clubs in the sport, went 13-14 in the month.

“Not our best month, obviously,” Aaron Boone said. “We know we have to be better. We have to find a way to finish some of these games.”

That task became more difficult on Monday when the Yankees put one of their best relievers, righthander Fernando Cruz, on the injured list with a left oblique strain. After Monday night’s game, Boone described testing on the oblique showing a “high-grade” strain.

“Obviously, that will be some time,” Boone said of how long Cruz might be out.

Additionally, Trent Grisham, who has played an excellent centerfield this season and ranks second on the team with 15 home runs, was replaced by Jasson Dominguez in the bottom of the fifth inning after feeling tightness in his left hamstring.

“Too early to tell,” Grisham said of his concern level. “We’ll see how it feels when I wake up in the morning.”

Cody Bellinger’s 12th homer of the season, a solo shot leading off the eighth off lefty Mason Fluharty, brought the Yankees within 5-4.

Aaron Judge was then intentionally walked and Jazz Chisholm Jr., who homered for the fourth time in his last five games earlier in the night (a two-run shot off Max Scherzer in the fourth inning), bunted Judge to second.

In came former Yankees reliever Chad Green to face Giancarlo Stanton, who walked. Green, who entered Monday having allowed 10 homers in 34 innings this season, retired Ben Rice on a flyout near the track in center and got Anthony Volpe to line out to right-center.

In the ninth, Toronto closer Jeff Hoffman allowed a two-out single to Dominguez before getting Bellinger to fly out to right for his 19th save in 23 chances.

Still, the game was almost entirely about the sixth inning, and though it didn’t compare with the fifth inning from Game 5 of last October’s World Series loss to the Dodgers, it contained plenty of ugliness.

With the Yankees leading 3-1, Davis Schneider doubled off Carlos Rodon to lead off the inning. Boone brought in Mark Leiter Jr. to face Myles Straw. The centerfielder hit a sharp grounder to short where Volpe made a sliding stop before making an errant throw to third trying for Schneider. Volpe was fortunate Schneider didn’t score on his team-high 11th error, though Straw took second on the play.

Pinch hitter Nathan Lukes’ RBI single made it 3-2 and, after Leiter struck out Will Wagner, the speedy Ernie Clement drove in a run with an infield single to short to tie it at 3-3. On the play, Volpe tried to throw out Clement on a ground ball in the hole, but Clement easily beat the throw to first and Lukes advanced to third.

Jonathan Loaisiga came in to face George Springer, who reached on a catcher’s interference call against J.C. Escarra — the Yankees’ second error of the inning — to load the bases. Vladimir Guerrero Jr., who brought a career .905 OPS against the Yankees in his career into the day, then smoked a two-run single to left to make it 5-3.

“We weren’t getting outs on those balls but obviously gave them an extra couple of bases,” Boone said.

Of Volpe’s decision trying for the out at third, Boone said, “I don’t have a problem going to third . . . we just have to be accurate with the ball.”

Volpe, who had 17 errors in his rookie season (winning the Gold Glove) and 16 last year, wasn’t down on himself.

“I think you look at a case-by-case basis,” Volpe said. “There’s obviously a lot of plays you want to have back and then there’s some plays you’re going to be aggressive. The error [Monday], I’m going to go for that play every single time.”