DENVER(AP) The Colorado Rockies ' celebration over Jason Giambi 's heroics quickly turned to concern over closer Huston Street 's ailing right arm.

Giambi's pinch-hit two-run single off Brian Stokes broke an eighth-inning tie and powered the Rockies to a 5-2 win over the New York Mets on Wednesday night.

But the crowd's cheers quieted when left-handed setup man Franklin Morales jogged out from the bullpen instead of Street, who has 33 saves in 34 chances.

''He has a little tightness in his biceps area,'' Rockies manager Jim Tracy explained. ''It was a little bit tight last night and it wasn't loosening up real good while we were rallying in the eighth inning.''

So, Franklin pitched the ninth for his first career save instead of Street, who said he initially blamed the tightness Tuesday night on having not pitched in a week.

''I didn't like the decision, but it was the right call,'' said Street, who had ice packs and a muscle stimulator on his biceps after the game.

''This late in the season you can't afford to mess up and be down two or three weeks when it might be only four or five days to a week if we just be smart about it and shut it down.''

Street said he hasn't had this kind of injury since high school but was confident that he was avoiding a longer layoff by not trying to work through the injury.

Giambi's first hit for the Rockies made a winner of Ubaldo Jimenez , who outdueled Tim Redding and kept Colorado atop the NL wild-card race by a game over San Francisco.

''That's one of the reasons I came here, to help this team down the stretch,'' Giambi said.

With the bases full and the crowd on its feet waving white giveaway T-shirts, Giambi, pinch-hitting for Clint Barmes , lined Stokes' first offering into center field just over the outstretched glove of a leaping shortstop Anderson Hernandez near the second base bag, making it 4-2.

''We had him played just right. Our shortstop wasn't tall enough,'' Mets manager Jerry Manuel said.

Giambi, who was jettisoned by Oakland this summer, signed with Colorado last week and was called up from the minor leagues Tuesday for just these kinds of circumstances. On Tuesday night, he walked on four pitches with the bases full. This time, he didn't hesitate to jump on the first strike he saw.

''I've seen him do that too many times,'' said Mets outfielder Gary Sheffield , who played with Giambi on the Yankees from 2004-06. ''He's a professional hitter. He doesn't panic in those situations.''

Giambi has said he doesn't mind going from full-time slugger to part-time player, one who's called upon for his clubhouse leadership as much as his late-inning at-bats.

''It's kind of a new experience for me, but at the same time I enjoy being in that spot,'' said the 38-year-old veteran. ''I'm thankful that the Rockies came calling and gave me this opportunity. ... Like I said, there are no small roles in a chance to win a pennant.''

Yorvit Torrealba followed Giambi's electrifying moment with a run-scoring single off Stokes (2-4), extending his career-best hitting streak to 12 games.

Jimenez (13-10), who went 5-1 with a 1.77 ERA in August, allowed two earned runs on five hits in eight spectacular innings as he worked at least into the sixth for the 24th straight time - and got the win to show for it thanks to Giambi.

''I knew he would deliver,'' Jimenez said. ''I knew he would come through and he did.''

Giambi has just as much praise for Jimenez, whose only mistake was a hanging curve that Jeff Francoeur deposited over the left-field wall in the second inning, his 12th homer tying the game at 2.

''You're looking at a future Cy Young winner,'' Giambi said. ''If he can get his whole game together: overpowering fastball, great stuff, great mound presence. Yeah, he's definitely one of those guys who has the potential to be phenomenal in this league. The ball explodes out of his hand.''

Tim Redding matched Jimenez inning for inning in his third strong start since rejoining the Mets' rotation Aug. 22. He surrendered two earned runs on seven hits in 6 2-3 innings with one walk and six strikeouts.

Seth Smith sent his 12th homer into the rock pile in straightaway center to tie it at 1 in the first inning.

NOTES: Mets slugger Carlos Beltran , sidelined since June 22 with a bone bruise on his right knee, began a minor league rehab assignment Wednesday night for Class-A Brooklyn. He went 1-for-3 with a walk and an RBI as the DH. ... Newly acquired RHP Jose Contreras threw a bullpen session Wednesday as he prepares for his Rockies debut Saturday night against Arizona.