BOSTON -- It's said that momentum in baseball is only as good as the next day’s starting pitcher. And it’s said because it’s true. Just ask the Boston Red Sox, owners of the fifth-worst starters’ earned run average in the major leagues, and a .500 record that proves just how much trouble they’ve had building on wins and sustaining success.

But if this team is ever going to figure it out, now would seem the time.

Desperately needing to go on a run in order to legitimize their chances of landing a wild-card playoff berth, the Sox had positioned themselves to do that. On both Sunday and Monday, they got good pitching, their best hitters lived up to their billing, and it produced a pair of wins.

Coming up Thursday they’ll make a four-day visit to Cleveland, where they’ll face an Indians team that had, through Monday, lost its last 10 games. It presented the Sox with an excellent chance to win something like seven of nine, a chance to start chipping away at a four-game deficit in their fight for a place in the postseason, a chance to finally get this season going in the right direction — if their starting pitchers could simply carry that momentum through Tuesday and today.

And that’s where Jon Lester and Josh Beckett come in.

For as disappointing as the duo has been this season — combining to go 10-18 with a 4.99 ERA over its first 40 starts — Lester took the mound Tuesday, and Beckett will take it today, with an opportunity to start the process of absolving himself of his sins.

None of that can be undone by just one outing, of course. But if the Red Sox are to make anything of this season, there’s reason to think that the start of their surge will be traced to this stretch — so after Franklin Morales and Aaron Cook each did his job, Boston’s two supposed stoppers took the ball with a chance to be at the forefront of any resurgence.

Lester turned that responsibility into his sharpest outing in a month, facing the minimum through four innings and then using a nasty cutter to tie up Geovany Soto and work around a single after a wild pitch put Michael Young in scoring position during the fifth. He varied his arsenal just enough to keep off-balance the Texas lineup that lit him up for seven runs in less than three innings at Fenway Park in April, but worked quickly and without wasting pitches.

The lefty ran into some trouble in the sixth, when Ian Kinsler followed David Murphy’s double with a wall-ball single, and Josh Hamilton scored Kinsler with a two-out rope — but although he trailed 2-0 at that point, Lester had done his job. He allowed six hits to the AL’s most prolific offense in 6 2/3 innings. He himself hadn’t given away the momentum stirred over the two previous days.

So now it’s Beckett’s turn. He’ll pitch this afternoon, and according to a Tuesday interview with a Boston rock station he will do so free of both back spasms and the anxiety he experienced when hearing his name mentioned before the trade deadline.

He has been OK against the Rangers this season, going seven innings in each of his starts, and allowing seven earned runs over those two outings — but it’s his third that could matter most, as it signifies his chance to break the cycle. To start changing the story.

And to give his Red Sox the momentum they badly need to maintain.

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MANAGER Bobby Valentine didn’t go into detail about the rest of his starting staff prior to the game, but by saying Cook would be held out of the upcoming Cleveland series, he effectively suggested the team will go with a six-man rotation at some point soon.

Felix Doubront and Clay Buchholz are slated to pitch the first two games against the Indians, with Morales and Lester presumably following. After that it would be Cook or Beckett in Baltimore on Monday, with the other pitching on Tuesday.

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AFTER having a pain-killer injected into the area of the aching heel that’s left him on the disabled list since July 16, David Ortiz could be activated at some point this weekend if all goes well over the next few days.

The designated hitter had initially hoped to return by now, but when he wasn’t progressing as quickly as it hoped from the Achilles’ strain, the team and the player decided to go with the shot. Once he has the ability to run at full speed, Ortiz should theoretically to jump right back into the lineup, as the designated hitter has been taking batting practice regularly — and barring another injury in the meantime, it would give the Sox a lineup featuring Carl Crawford, Jacoby Ellsbury, Dustin Pedroia and Ortiz for the first time since last September.

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SAYING a second opinion suggested the condition had existed for a while, Sox reliever Scott Atchison will attempt to rehabilitate while dealing with a tear in his elbow rather than go through Tommy John surgery to have it reconstructed. He hopes to be back at some point next month. At this point, surgery would cost him most of next season.

Dave D’Onofrio covers the Red Sox for the New Hampshire Union Leader and Sunday News. His email address is ddonof13@gmail.com.