BOSTON — That sigh of relief belonged to David Ortiz.

When Ortiz crushed a 3-and-0 fastball from Toronto starter Dustin McGowan into the Blue Jays’ bullpen in the first inning last night, the blast snapped a long home-run drought at Fenway Park for the Boston Red Sox’ powerful designated hitter.

The dry spell lasted for 129 at-bats spread over 34 games, since he had taken the Yankees’ Jeff Karstens deep on April 21.

Ortiz’s home run was not the major blow in the Red Sox’ 9-4 victory over the Blue Jays. That honor belonged to catcher Jason Varitek, who, in the sixth inning, clouted a long tie-breaking two-run homer into the bleachers just above the Boston bullpen where it forms the triangle in center field.

Varitek’s homer gave the Sox a 6-4 lead, moments after Daisuke Matsuzaka had surrendered three runs in the top of the inning, surrendering a three-run advantage in a mediocre, 110-pitch outing.

The Sox ultimately pushed across five runs in the pivotal sixth-inning outburst, using speed (bunt single by Julio Lugo, double steal by Coco Crisp and Dustin Pedroia) and productive hitting by Pedroia (single), Manny Ramirez (sacrifice fly) and Kevin Youkilis (single), each of whom produced a run in opening up the game for Boston.

But probably the best news to come out of last night’s game was the resurgence of Ortiz at the plate. Not that he hadn’t been a solid hitter all season. He entered last night’s game batting .318. Ortiz, though, has not been generating home runs, partially because of a torn meniscus in his right knee, a problem he disclosed after Thursday night’s game.

Ortiz, who set a club record with 54 homers last year, was stuck on 14 — only three at home — when he stepped into the batter’s box in the first inning last night.

Thanks in part to some advice and video work done by hitting coach Dave Magadan, the ball was jumping off Ortiz’s bat last night. In addition to the homer, Ortiz launched a run-scoring, ground-rule double over the head of right fielder Alex Rios in the third and ripped a liner right at Rios in the eighth.

“I’ve been having problems with my swing all year,” said Ortiz. “I’ve been battling through this and that, like my knee. I use my legs a lot. That’s how I create my power. It (the swing) kicks in and kicks out. Even in batting practice I’m serious with my swing. I try to take what I do there into the game. But even in BP, I wasn’t driving the ball.

“I’m trying to use my hands more. When I got to the park today, Mag (Magadan) brought me to the videos,” he said. “We went over some stuff that I put into play in the game. Every time I took a swing (last night), I’d look at (Magadan) and I was like, ‘Dude, we should have done that three months ago’ ” joked Ortiz.

Ortiz decided not to wait around in the first inning. When the count reached 3-and-0, he was ready.

“I was swinging at it. That might be the only time you see a pitch (to drive) all night. You don’t want to waste it,” said Ortiz.

He didn’t. He watched intently as the ball cleared the fence, finally able to show off his home-run trot at home.

“It won’t be 129 at-bats (before another one at home). I guarantee it,” said Ortiz, who is 6-for-13 (.462) with two doubles, a homer and four RBI in the three games since the break.

Manager Terry Francona certainly has liked what he has seen from his slugger in the second half.

“The way he has swung the bat the last few games, just driving the ball and staying through it, if he swings like that you’ll see a lot of balls leaving the park,” said Francona, who before yesterday’s game offered to give Ortiz more rest here and there, an offer Ortiz is passing on for the time being.

While Ortiz was returning to form, Matsuzaka was suffering through a second straight so-so performance.

The right-hander from Japan was tagged for nine hits, six of which were for extra bases, including back-to-back doubles by Frank Thomas and Troy Glaus and a two-run homer by Aaron Hill in the sixth as the Blue Jays pulled even at 4-4.

In his last start of the second half, Matsuzaka was cuffed for 10 hits and six runs in only five innings in a loss in Detroit. Over his last two starts, Matsuzaka has given up 19 hits — 12 for extra bases, including five home runs. His earned-run average for those starts, which have come on the heels of six excellent outings, is 8.18.

Yesterday, in an effort to get better command of his pitches, especially his fastball, Matsuzaka pitched a few innings from the stretch even though there was nobody on base.

“It’s something I’ve done in Japan, one of the things I do to improve my balance,” said Matsuzaka, who, backed by the big sixth-inning explosion, improved to 11-6.

“It’s something I do to try to make adjustments. I was hoping to see some improvement after that point, but I wasn’t able to do that today,” he said.

skrasner@projo.com