BOSTON -- The Detroit Tigers' offense had squandered excellent outings by their starting pitchers on Thursday and Friday.

They weren't about to do that three games in a row.

Led by third baseman Alex Castellanos' two hits and three RBIs, the Tigers made sure right-hander Alfredo Simon's six-plus strong innings and shutout work from their bullpen stood up Saturday in a 5-1 victory against the Boston Red Sox at Fenway Park.

The Tigers (48-49) had lost their previous two games despite getting eight innings from David Price (two runs allowed) and Justin Verlander (one run). The Tigers scored three runs in 23 innings in those two defeats.

"It's been better," Tigers manager Brad Ausmus said about Detroit's starting pitching. "Unfortunately we didn't take advantage of two of them. That's the problem. But today we were able to take advantage of a good outing by Simon."

Only a slight groin injury shortened Simon's outing, as he pitched into the seventh inning but left with an 0-2 count on leadoff hitter Pablo Sandoval. Simon, who had allowed 20 runs in 19 1/3 innings in his previous four starts, allowed one run on five hits against Boston. He walked two, struck out four and threw 48 strikes among his 83 pitches.

Simon (9-6) said his improvement was helped by harkening back to when he started the season 4-0 in April and some of his other strong early-season starts.

"I just tried to look at my video from three months ago, two months ago. And then every time when I throw the ball down and my two-seamer works and my split, everything came through," Simon said. "So I feel happy today. I'm back the way I was, so I'm really happy."

Said Ausmus: "I think he used his fastball well. He threw a lot of splits, but he used his fastball to get outs."

Outfielder Yoenis Cespedes gave the Tigers' slumping offense an early lift by hitting a solo home run with two outs in the first inning against knuckleballer Steven Wright (3-4).

"I mean it's comfortable, you know. And for Simon to go out there with an early lead, it's reassuring," Castellanos said. "And then also just because he's a knuckleball pitcher and you kind of see that, it gives the rest of us kind of confidence to know that, 'All right, maybe it's hittable today.' Because, with a knuckleball, it's just a guessing game -- because when it's on, it's pretty hard."

The Tigers scored one run in the second inning without getting a hit and two in the fourth inning, along the way taking advantage of Red Sox catcher Blake Swihart's four passed balls. In the second inning, Tigers outfielder J.D. Martinez walked and took second on a passed ball. He went to third when first baseman Alex Avila reached base on a passed ball after a strikeout. Catcher James McCann drove in J.D. Martinez with a fielder's choice groundout.

Designated hitter Victor Martinez and J.D. Martinez started the fourth inning with singles. They moved up to second and third on another passed ball and both scored on Castellanos' double, which gave Detroit a 4-0 lead.

Swihart, who has caught Wright's knuckleball both in the minors and majors, had six passed balls on the season before Saturday.

"(Wright) did a great job today throwing the ball," the rookie catcher said. "My job as a catcher is knock it down any way I can, and I didn't do a very good job."

Boston (43-55) scored its only run on an RBI groundout by Mookie Betts in the bottom of the fifth inning. In the top of the sixth, Castellanos' home run off reliever Noe Ramirez extended the lead to 5-1.

Relievers Ian Krol, Alex Wilson and Joakim Soria combined for three scoreless innings of relief to send the Red Sox to their ninth loss in 10 games.

Simon, who first felt the groin injury in the fifth inning when fielding a David Ortiz ground ball, said he's confident he'll be able to make his next start. The Tigers are enjoying the starts their getting from their pitchers.

"It's the starting rotation that we know we have, you know. And I guess it makes our job easier as the lineup to know that 'Let's just put together some good AB's, get a couple of runs and we can come out with a victory," Castellanos said. "Obviously it didn't happen the past two days, but hats off to the starting rotation because they've been doing a great job."

NOTES: Red Sox 2B Dustin Pedroia went on the 15-day disabled list with the same right hamstring strain that landed him on the DL from June 25 through July 17. Pedroia, who sat out the two games before Saturday, was 1-for-22 in six games since his return. Manager John Farrell said there was no timetable for Pedroia's return. ... Tigers INF Miguel Cabrera, who has been on the DL since July 4 with a left calf strain, continued to make progress toward a return, although manager Brad Ausmus said Cabrera was still far from ready to play in a game. But Cabrera has taken batting practice, run on a treadmill and practiced at first base. ... Tigers pitcher Shane Greene will look to snap a personal five-game losing streak when he faces the Red Sox on Sunday. Greene, 0-5 in his past six starts, hasn't won since he beat the St. Louis Cardinals on May 15. ... Pitcher Pedro Martinez, who is tied for sixth on the Red Sox all-time list with 117 wins, will be inducted into the Baseball Hall of Fame on Sunday.