BOSTON — Health has been Jon Lester’s one constant amid his struggles. So when Lester walked off the mound in the middle of an at-bat in the eighth inning on Thursday, the Red Sox’ worst fear flashed before their eyes.

Fortunately for the Red Sox, they can breathe easy. Not only is Lester OK, but he also turned in his best performance in over a month as the Red Sox earned a 7-4 win over the Blue Jays.

Lester jammed his hip while delivering a pitch to Emilio Bonifacio in the eighth inning, and John Farrell wasted no time in taking out his starter. Lester said that he felt a “zinging sensation” after throwing the pitch, but he insisted that he felt normal shortly after exiting the game.

“I’m not too worried it,” Lester said. “The docs didn’t seem worried about it and I’ll come in tomorrow and figure it out, but the way I’m figuring is I’ll pitch on my normal turn, maintain it and see how we go.”

Eighth-inning scare aside, Lester’s start against the Blue Jays was very encouraging, even if the final line score doesn’t come off as all that glamorous. Lester was charged with four earned runs on five hits over seven innings — with two runs scoring in the eighth inning after he was relieved by Junichi Tazawa — but he remained in control throughout the outing.

“Fastball command was pretty good tonight. I had a pretty good changeup. We were able to mix the ball in and out,” Lester said. “Obviously having a seven-run lead in the second inning helps. The offense did a good job of getting their guy out of there early and getting to that bullpen, especially with the four-game series so that was big.”

Lester’s night was certainly made easier by the Red Sox’ seven-run offensive outburst in the second inning, but the lefty showed a lot of improvement. In addition to his enhanced fastball command and good feel for his changeup, Lester was able to finish off innings — something that’s been a problem of late.

Lester didn’t allow a hit until the fifth inning — an inning in which he surrendered two runs on three hits — but he walked a couple of hitters early on. He stuck with it in each instance, and he managed to escape any damage until the fifth. Edwin Encarnacion grounded into an inning-ending double play in both the first inning and the fourth inning.

Even when Lester did stumble briefly in the fifth inning, he still responded well. Following Maicer Izturis’ two-run double in that frame, Lester retired seven straight to regain control of the game and work into the eighth inning.

Thursday’s start was Lester’s longest since May 25, when he also went seven innings. And although Lester didn’t end up recording an out in the eighth inning, it was the first time that the left-hander worked into the eighth since May 10, when he pitched a complete-game shutout against the Jays.

“I feel that responsibility to go out there and save the bullpen and that’s what I tried to do tonight,” Lester said. “Obviously, I would have liked to have given Taz a little better situation than what he came into but I kept us in the game.”

Lester can now hang his hat on back-to-back wins. They haven’t been perfect — or without a brief scare — but strides are being made.

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