For the five innings last night, Beckett appeared to have turned the corner. He looked powerful against the Angels, with a good command of his fastball.

Then came the sixth and the fastball to Hideki Matsui that was supposed to be down and away but instead was middle and in. It was gone.

Beckett’s chance to help the Sox complete a season sweep of the Angels went with it, turning a tantalizing first five innings into a 7-2 loss.

“You don’t make pitches, you don’t get outs,’’ Beckett said.

The first time through the batting order, Beckett allowed one single and one walk. The second time through he gave up another single. It all fell apart the third time through, with the Angels going 5 for 9 with one homer, two doubles, and two singles, as they got seven hits and six runs off Beckett.

“Beckett was really coming out with that fastball, he was explosive today,’’ Angels right fielder Torii Hunter said. “The second and third time around we kind of calmed down a little bit and tried to get pitches in the zone and be ready for the fastball. We were able to jump on it.’’

After Beckett got a groundout to begin the sixth, he gave up doubles to Maicer Izturis and Alberto Callaspo, for a 1-1 tie. Beckett still seemed in control, even after he gave up a laser of a single to Hunter, which bounced off Adrian Beltre and into foul territory.

But all it took was one awry fastball to Matsui, who deposited it into the Sox bullpen for a three-run homer. The Sox wouldn’t recover, not with Ervin Santana throwing seven-plus strong innings (two runs, four hits).

“The last couple [of Beckett’s] outings haven’t been like the first three since coming off the disabled list. Tonight there were a lot of encouraging signs in there coming out of the game in New York and then down in Texas,’’ pitching coach John Farrell said. “But the way Santana was pitching, a four-hitter stretch, particularly the first-pitch fastball to Matsui, that right there was the difference in the ballgame.’’

Beckett repeated that the problem was his fastball command. That was the reason he didn’t make it past the fifth inning in his last two starts. He was more pleased with last night’s first five innings, though not quite so much after that.

“His fastball was down in the zone,’’ Farrell said. “He threw some curveballs that he was able to finish some hitters off with. I think that’s been one of the more encouraging signs, is that in the six starts that he’s had since coming back, his curveball has shown more consistency, more of a true weapon. [I] thought he was down in the zone for the most part with his fastball, except for the sixth inning.

“I think it’s going to be key for him to recognize there were a lot more positives than maybe the linescore indicates.’’

Yet the six or more runs given up in each of his last three games marks the longest such streak in his career.

“The hope is that he can build off of what he did positive and not let the sixth get in the way of the rest of the season, cause he was really good,’’ said manager Terry Francona.

The Sox weren’t generating much offensive support. David Ortiz had blasted a solo home run just beyond the bullpen in right-center in the fourth, for a 1-0 lead, pushing his hitting streak to 10 games. But Santana shut down the Sox after that. By the time Santana came out for the sixth, now with a 4-1 lead in his pocket, the pitcher had allowed just two hits.

Much of the damage had already been done by the seventh inning, but that inning turned ugly, an example of what the Sox are not getting from reliever Manny Delcarmen.

After Beckett struck out Jeff Mathis to lead off the inning, he allowed an infield single to Peter Bourjos, walked Bobby Abreu, and was removed from the game. Delcarmen walked three of the four batters he faced, including one with the bases loaded.

“Hadn’t seen that for a while,’’ Francona said. “His arm wasn’t catching up, and there was obviously not enough strikes, missing in the same place and repeating it led to trouble.’’

In the end, though, it is Beckett who is crucial to this team, and their chances this season and beyond. Not that anyone wants to make it all about him.

“You can’t put that kind of pressure on,’’ Sox catcher Victor Martinez said. “We still have four more guys out there that can go out there and give us a good chance to win games. He’s a human. Everybody can’t be perfect. It happens.’’