BOSTON — With Clay Buchholz hurt and Jon Lester struggling, the Red Sox need John Lackey to come through to keep the team out front in the suddenly crowded American League East standings.

And Lackey continues to come through.

The veteran righty, making an impressive comeback from last year’s Tommy John surgery, matched his career high with 12 strikeouts, leading first-place Boston to a 5-3 victory and a sweep of a two-game interleague series with the Colorado Rockies on Wednesday.

“It seems like as, either through the injury or through some performances that have been a little inconsistent, we’ve had some guys step up and John has been one of the mainstays right now over really the last month,” manager John Farrell said after Lackey went seven innings and didn’t walk anyone. “Felix [Doubront] continues to come along in his own right, but John led the way today.

“It was good to go out and get three runs in that first inning, give him a little bit of a cushion; top of the order once again did an excellent job getting on base but at that point turned it over to John and he was outstanding.”

Lackey (5-5) allowed two runs on eight hits in his third straight seven-inning, two-run performance. He lowered his ERA to 2.99 with his fifth straight outing without a loss. He has issued just three walks in those five starts.

His fastball was clocked at 95 mph early in the game. Farrell said it was “probably the strongest he’s been all year.”

Lackey and fellow veteran Ryan Dempster, who beat the Rockies on Tuesday night, are helping the Red Sox stay atop the American League East in a big way.

“Jon will be fine and Clay healthy obviously has done great,” Lackey said. “I’m not worried about those guys at all.

“Demp’s been in the league, what, 15 years? And I’m working on 12. We’ve seen a few things and one of the things that we bring is you kind of know what you’re going to get. It’s stability. Most of the time we’re not going to beat ourselves, we’re going to make the other team come and get us if it does happen.”

Daniel Nava drove in two runs and Shane Victorino had three hits and scored twice for Boston, which had 30 hits in the two games against the Rockies.

Michael Cuddyer, who extended his hitting streak to a career-high 23 games to tie current Colorado hitting coach Dante Bichette’s club record, hit two solo homers for the Rockies, who have lost seven of their past nine games to fall back under .500.

“We’re not going to sit and think about this road trip,” said manager Walt Weiss. “We’ll show up at Coors tomorrow [a makeup game against the Mets] and try to win that game. The next day we’ll do the same thing.

“We’ll just keep grinding along.”

Cuddyer opened the sixth inning with his first home run of the game. He also led off the eighth with his 13th homer of the year.

Koji Uehara, the closer with Andrew Bailey struggling, pitched a perfect ninth (with Boston’s 14th and 15th strikeouts of the game) for his second save of the season.

Roy Oswalt, who fell to 0-2 in two starts with the Rockies, gave up five runs on nine hits in six innings. He has 16 strikeouts in his two outings.

“Bodywise I feel pretty well,” he said. “See how it goes the next one.”

After the Rockies scored in the first on the first of two Carlos Gonzalez hits, a stolen base and two-out single by Wilin Rosario, the Red Sox went ahead to stay with their three in the bottom of the inning.

Jacoby Ellsbury opened with a double and scored on Victorino’s single. David Ortiz doubled Martinez home, took third on a groundout and scored on Nava’s single.

NOTES: Buchholz, who was having a Cy Young-type season (9-0, 1.71 ERA) but hasn’t pitched since June 8, was unable to go deep into a bullpen session Wednesday and was sent for an MRI (no results announced). He had hoped to make a rehab start Sunday or Monday. “It’s not anything that I couldn’t go out and pitch with, but it’s sort of the same thing I felt the first time I missed a start,” he said. “I felt fine against the Yankees (June 2) and then it had to be that throw I made in an awkward position (June 8). That’s sort of where I’m at right now.” … Cuddyer has also reached base in a club single season-record 42 straight games. … Mike Napoli had a bases-loaded single in the third inning and is 7-for-12 with two homers and 20 RBIs with the bases full this season. He has 53 RBIs, just three fewer than he had all last season with Texas. CF Dexter Fowler was out of the Colorado lineup with a sore wrist. His replacement, Tyler Colvin, struck out four times. … The Sox activated RHP Clayton Mortensen (groin) from the DL and returned RHP Pedro Beato to Pawtucket and have had 27 transactions since June 8. … RHP Tyler Chatwood (4-1, 2.22 ERA) starts the Rockies’ makeup home game against the Mets Thursday, while Lester (7-4) faces the Blue Jays in Boston’s opener of a four-game home series Thursday night. Lester pitched a one-hit shutout against Toronto May 10 at Fenway Park. … Paralympic gold medalist Victoria Arlen threw out the ceremonial first pitch. … Colorado first base coach Rene Lachemann, who used to coach third for Boston, is in his 50th consecutive year in professional baseball, as a player, coach and manager.