The Houston Astros’ Miguel Tejada, center, scores the game’s go-ahead run on a single by Mark Loretta in the eighth inning against the Red Sox as the Astros’ Humberto Quintero looks on yesterday. Sox catcher Jason Varitek stands at right.

AP / Bob Levey

HOUSTON — Talent evaluators in baseball all agree — trying to forecast how middle and set-up relievers will fare from one season to the next is next to impossible.

Case in point: Hideki Okajima.

A year ago, Okajima was a shutdown set-up man for the Red Sox, expertly stranding 24 of 28 inherited runners while recording key outs in the eighth and ninth inning.

This season, however, Okajima has stumbled when it comes to stranding runners. For the last six weeks, the Sox had studiously avoided bringing Okajima into games with runners on base.

Not since May 14 — when he served up a game-winning grand slam to Jay Payton — had Okajima been brought into a game with runners on base. But yesterday, tied 2-2 with the Houston Astros in the eighth inning, the Sox ran out of options. With the bullpen spent from Saturday’s slugfest and wanting to turn around switch-hitter Geoff Blum, the Sox summoned Okajima from the bullpen with Miguel Tejada on first and one out.

Okajima promptly threw a wild pitch to put the potential go-ahead runner in scoring position. Then after getting Blum on a comebacker, Okajima surrendered a sharp single to center to pinch-hitter Mark Loretta, scoring Tejada with the winning run and sending Minute Maid Park into delirium for a 3-2 Astros victory and series win.

Okajima has inherited 15 runners this season and 12 — or fully 80 percent — have come around to score.

“He actually made some really good pitches to Loretta,” Francona said of Okajima. “But then he left a split over the middle.”

The Sox had been habitually bringing Okajima only to start innings fresh, in the hope of restoring his confidence with some less-stressful outings.

“There are times,” Francona said, “regardless of what I said a month ago, that we need to get outs. It didn’t work today … When guys go through frustrating times, we can’t run from them.”

When Tejada crossed the plate yesterday, it marked the 11th time in the last 12 situations that Okajima had failed to strand an inherited runner.

Okajima, as has been his custom after contributing to losses, declined to speak to reporters, telling a Red Sox public relations official that he had “nothing to say.”

The defeat was the first interleague road series loss for the Sox this season and saw them drop a three-game set to a team battling to stay out of the National League Central cellar.

It also dropped them into second place as they begin what few could have imagined back in April: a battle for first in the division with the Tampa Bay Rays.

Beyond the loss, there was the frustration for the Sox yesterday of having wasted another gem from starter Josh Beckett, who limited the Astros to just two runs over seven innings, during which he threw 108 pitches.

“Too many pitches,” said Beckett of his effort. “I’ve got to count down on those three-ball counts.”

Beckett walked only one hitter, but ran his count up so that he was out after seven.

Then again, in providing just two runs with which to work for Beckett, the Sox’ offense continued a disturbing pattern.

Yesterday marked the sixth time in 15 starts this season that the Sox scored two runs or fewer while Beckett was in the game.

Beckett, conversely, has allowed three runs or fewer in seven of his last eight road starts, pitching to a 2.65 ERA, but has won only three of those eight outings.

The Sox got little done in the early innings against retread Brian Moehler.

They loaded the bases in the first, but left them that way when Youkilis grounded to second.

In the third, after Pedroia’s leadoff homer, the Sox used singles by Ramirez and Youkilis to give them two on with two out. But Jason Varitek flied to right, ending the inning.

For the afternoon, the Sox stranded 13 runners.

“We left so many men on,” Francona lamented. “We had more than a couple of chances (to break the game open early).”

The lone runs came on solo homers — one from Dustin Pedroia in the third and one from Manny Ramirez in the seventh.

Blum gave Houston a brief lead with a two-out solo homer to right in the second when Beckett had to come in with a fastball on a 2-and-0 pitch.

The only other run off Beckett came in the fifth.

Beckett had committed the mistake of walking Moehler with one out. A fielder’s choice from Michael Bourn erased Moehler, but the inning continued with an infield hit by Hunter Pence, giving the Astros runners at first and second.

Carlos Lee then drove a shot just past Beckett’s outstretched glove into center, scoring Bourn.

smcadam@projo.com