DENVER -- At the beginning of the season, left-hander Jorge De La Rosa was low on the list of players the Rockies trusted in tough times.

De La Rosa went 0-6 with a 5.43 ERA in his first 10 starts. In fairness, the Rockies scored three or fewer runs in half of them. But De La Rosa had enough bad innings to keep alive a reputation for not being able to prevent innings and games from spiraling out of control.

Pulse
Rockies at a glance
2009 record: 92-70
2008 record: 74-88
Clinched NL Wild Card
NLDS matchup:
Rockies at Phillies
Postseason tix: Information

WHO ARE THESE GUYS?
Gonzalez: Bat on fire
Bullpen: Hitting stride
Gonzalez: Rewarding Rox
Giambi: Impact beyond bat
Tulowitzki: Ready for return
Cook: Returns right on time
Barmes: Credit to Tracy
Marquis: Living in moment
Ubaldo: Big-game pitcher
Helton/Giambi: Leaders
Stewart: Emerging star
Tracy: Quiet leader
Street: Mutual admiration
De La Rosa: Earning trust
Ubaldo: Sending a message
Helton: Resurgent slugger
Morales: On the attack
Tulowitzki: Vigorous finish

Since June 5, however, De La Rosa is 15-3 with a 4.01 ERA in 21 starts. No National League pitcher has that many wins in that period. Sunday afternoon -- in the finale of a three-game set with the Cardinals -- will mark the second time in three starts that De La Rosa will receive the ball in a start of great importance to the Rockies.

"I'm excited for everybody," said De La Rosa, who can provide a fastball above 95 mph and a swing-and-miss slider -- a combination that has made him successful, and could make him famous if the team reaches the postseason and advances. "If we make the playoffs, it's going to be my first playoffs. I'm so glad to be in this position right now."

Last time the Rockies really needed him, it worked out nicely.

The Rockies entered De La Rosa's Sept. 16 start against the Giants having dropped two straight to San Francisco, then their closest competitor for the NL Wild Card. But De La Rosa responded by throwing eight scoreless innings, with eight strikeouts, in a 4-3 victory.

But any stumble needs new questions about his ability to handle adversity.

In his last start at Coors Field on Tuesday night, De La Rosa gave up eight runs in three innings in the club's 11-10 victory over the Padres. If the preponderance of De La Rosa's work this season demonstrates how much he has grown, the odd game like Tuesday is an illustration of why the D-backs and Red Sox let him go before he reached the Majors, and why he never established himself with the Brewers and the Royals.

But these days, De La Rosa, 27, is a picture of confidence. The Rockies acquired him from the Royals for cash early last offseason. After being in and out of the rotation, De La Rosa showed growth during a second half that saw him go 9-2 with a 3.47 ERA in his final 13 starts.

De La Rosa connected with pitching coach Bob Apodaca. He also worked on his psyche with Rockies performance-enhancement coach Ronn Svetich. When Svetich gave written materials to De La Rosa, a native of Mexico who is comfortable with Spanish, De La Rosa's wife would translate them.

So, going into Sunday, with the Rockies holding a 2 1/2-game lead over the Braves in the NL Wild Card race, De La Rosa believes he has the foundation to handle the big game.

De La Rosa said the problem in his last start was simply rushed mechanics. It has cropped up several times this season, but more often than not, he has corrected it before letting his start unravel. De La Rosa expects the last start, during which manager Jim Tracy said he stopped pitching and started throwing, to be an aberration.

"My arm feels very good," De La Rosa said. "I've got much better control on all my pitches, and that's helped me a lot. I'll try to do the same thing in the next two games I have left and try to make the playoffs and get ready for it.