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The staggering New York Mets are shutting down an ace and trying to groom their next one.

Hours after Johan Santana was placed on the disabled list, prized rookie Matt Harvey gave the Mets another bright glimpse of the future with his latest impressive outing during New York's 5-2 loss to the Colorado Rockies on Wednesday night.

Harvey struck out nine over six innings of three-hit ball, giving him 43 strikeouts through his first six major league games. The Mets said that broke Nolan Ryan's previous club record of 42, according to research by the Elias Sports Bureau.

"Extremely impressed tonight with the way he handled himself, pitching out of trouble, electric stuff again," Mets manager Terry Collins said. "He asks all the right questions. He pays attention. He's the first guy on the bench before the game starts. He's there throughout the game. He listens. He wants to learn. He truly is living up to that, 'I'm not here to be one of the guys. I'm here to be THE guy.' We think we've got some more coming. During an absolutely brutal stretch, there's been a bright spot, and he's been one of them."

Drafted seventh overall in 2010, Harvey is no slouch at the plate, either. He went 2 for 2 with a pair of singles and is batting .455 (5 for 11) with two doubles and two RBIs.

On the mound, the 24-year-old right-hander walked two and lowered his ERA to 2.75 in 36 big league innings.

"He's really good. We have to stay positive on that note, for sure. He's throwing the ball really well," catcher Kelly Shoppach said. "He's got something special going."

Harvey's best efforts weren't enough for the Mets, though. Wilin Rosario hit a tiebreaking homer in the seventh inning, and the Rockies went on to their seventh straight victory at Citi Field.

Rosario also had a sacrifice fly, and DJ LeMahieu drove in a run with a squeeze bunt to help the last-place Rockies win their fourth in a row and eighth in 10 games before a sparse crowd of 22,204. Colorado will go for a four-game sweep on Thursday, a feat the Rockies accomplished during their previous visit to Queens in April 2011.

The slumping Mets (57-67) lost their fourth straight and fell to 11-27 since the All-Star break, leaving them 10 games below .500 for the first time since finishing 70-92 in 2009. They've been held to two runs or fewer in five consecutive games for the first time since September 2003.

With two runners on in the ninth, Ronny Cedeno flied out to the left-field warning track to end it.

"I feel like there's more that I could've done and more I could've helped the team with — like going eight innings and not giving up a run would've been nice," Harvey said.

Before the game, the Mets placed the struggling Santana on the 15-day DL with inflammation in his lower back and said he isn't expected to pitch again in 2012. Doctors recommended rest, but not surgery.

The 33-year-old Santana, who missed last season following major shoulder surgery in September 2010, went 0-5 with a 15.63 ERA in his final five starts.

Colorado's Jeff Francis allowed one run and five hits in a five-inning start, though not all the news was good for the injury-ravaged Rockies. Center fielder Dexter Fowler left in the fourth inning with a sprained right ankle after twisting it while cruising into second base.

X-rays were negative, but manager Jim Tracy said Fowler is likely to miss at least a couple of days.

New York cut it to 3-2 in the eighth. Scott Hairston, who had a sacrifice fly in the first, hit a two-out double off winner Carlos Torres (2-1) and scored on Ike Davis' single against Matt Reynolds. Will Harris, however, struck out pinch-hitter Jordany Valdespin to preserve the lead.

Colorado added a pair of insurance runs in the ninth, aided by Shoppach's throwing error and reliever Frank Francisco's balk. Chris Nelson had an RBI single, and pinch-hitter Josh Rutledge delivered a run-scoring double.

"It's another night, just like last night, where we did a great job with situational at-bats," Tracy said. "We hung in, and when we needed to execute offensively to produce some runs, we did so."

Back in the dugout, a frustrated Francisco gave a hard shove to the water cooler.

Rafael Betancourt worked a scoreless ninth for his 25th save in 30 attempts.

Rosario connected off Ramon Ramirez (2-3) leading off the seventh. The rookie catcher lofted a high fly into the left-field corner for his 20th home run to give the Rockies a 2-1 lead.

Tyler Colvin then doubled, moved up on a groundout and scored on LeMahieu's nicely executed bunt.

Torres yielded one hit in 2 2-3 innings.

NOTES: LF Jason Bay was booed all night. He has 11 hits in 105 at-bats since June 8. ... New York is 2-13 at home since the All-Star break. ... Mets RHP Jeremy Hefner and his wife, Sarah, had their second child, a baby girl they named Jaylee.