In the previous two seasons, Martín Pérez allowed just two runs over three starts against the Blue Jays. On Sunday, they dealt Pérez more damage than that in a single swing.

The lefty surrendered three long balls -- including a first-inning, three-run homer over the Green Monster -- and was pulled in the second inning of an 18-4 loss at Fenway Park. The onslaught included season-high allowances from the Red Sox in runs, hits (20) and extra-base hits (11), as well as a franchise-record eight home runs.

• Box score

“It’s gonna happen, games like this,” said Pérez, whose five runs allowed came on a season-high three home runs. “Once a year it’s gonna happen, and it happened tonight to us.”

Boston should hope that this type of loss comes once a year at most, but the disheartening results from its rotation are becoming far too common.

“It’s been a horrible week for us, pitching-wise,” Red Sox manager Alex Cora said. “For us to keep going and stay where we are [in playoff position], we have to pitch. Obviously a bad week. Two good hitting teams, but that doesn’t mean anything; we’ve faced some good hitting teams before and we did the job. It’s one of those that we’re grinding right now.”

In its past six games, Red Sox starters are 0-4 with a 12.00 ERA (32 runs in 24 innings). Two of those starts now belong to Pérez, which is hardly a trend on its own; but where Pérez had a chance to bounce back on Sunday, he landed in a deeper heap of trouble instead.

With two on and one out in the first, a middle-middle changeup from Pérez soared into the left-field seats, courtesy of Teoscar Hernández. Lourdes Gurriel Jr. homered two batters later, and Marcus Semien landed a ball on the batter’s eye with one out in the second inning.

Home runs have not been a notable nemesis for Pérez this season, as he entered the day having allowed just five in 60 1/3 innings. The Blue Jays stung three over the wall against the lefty, but in fairness they were hitting nearly everything hard: Of the 10 balls in play against Pérez, eight carried an exit velocity in excess of 95 mph.

“I’m not locating the ball where I want it,” Pérez explained. “It’s still early, man. We just need to make an adjustment, and just go out there and throw zeroes.”

Poor location is an apt assessment of how Pérez struggled, as the home run balls to Hernández and Semien were both center cut. From a staff-wide perspective, pitching coach Dave Bush believes poor pitch execution is the primary concern; but if that’s the effect, what’s the cause?

Could it be a matter of fatigue, now that teams are roughly a week past the 60-game mark?

“All the starters and probably most of the relievers have passed their innings total from last year,” Bush said. “There’s gonna be some natural dips along the way, and I’m sure that’s part of it.”

The Red Sox have seen the Astros and Blue Jays for the past six games, and those teams rank first and second, respectively, in team OPS (.789 and .781). Boston also hasn’t had an off-day in two weeks, and its pitching staff has been stretched thin since then.

Then there’s the increased public attention around “sticky stuff” and the conversation around whether pitchers who have struggled of late could be having poor outings due to a related change in habits. As it pertains to the Red Sox, this claim was quickly shot down by Pérez.

“I’m not a cheater pitcher, man. I’ve been around for a long time and I don’t use that kind of stuff,” he said. “We’ve been not pitching good for the last three or four days, it’s [not] because of the sticky things, no. It’s because we’re not locating the pitches where we want it.”

Cora backed his pitcher, saying he doesn’t see any relation between his rotation’s recent struggles and the recent focus on substances used by pitchers.

“No,” Cora said, “I just see the relation that we’re leaving a lot of pitches right down the middle and those guys are taking advantage of it.”