DENVER -- The move came in January, an obscure off-season transaction of seemingly minimal consequence. Seeking pitching depth, the Washington Nationals signed veteran Ross Ohlendorf to a minor-league contract. Nationals general manager Mike Rizzo knew him well, having been Arizona's scouting director when the Diamondbacks drafted Ohlendorf in 2004.

That little-noticed move paid a huge dividend Wednesday for the Nationals in their 5-1 victory over the Colorado Rockies.

Ohlendorf, 30, had spent the entire 2013 season before Wednesday at Triple-A Syracuse. But with a need for a starter when a rainout Friday forced a doubleheader Sunday, the Nationals turned to Ohlendorf. He pitched six innings, allowing the Rockies two of their three hits and their lone run.

"It's not easy in this ballpark; just an outstanding job," Nationals manager Davey Johnson said. "I'm going to try to find a way to keep him around."

Ohlendorf has pitched in plenty of parks during his big-league career. He has made 70 starts during stints with the Yankees, Pirates and Padres.

His numbers at Syracuse were pedestrian at 4-5 with a 4.27 ERA in 13 games, including 12 starts. But in his three most recent starts, he was 1-0 with a 1.56 ERA.

This year, Ohlendorf turned to an over-the-head, old-style delivery, which he credits for some of his success.

"It helps," he said. "It gives me rhythm and helps me stay loose. And the ball has been coming out well."

His new delivery allowed Ohlendorf to stymie the Rockies while the Nationals built a 4-0 lead thanks to a three-run sixth inning, driving Jorge De La Rosa from the game.

The rally began when Jeff Kobernus walked with one out and scored on Ryan Zimmerman's double to left-center. Left fielder Carlos Gonzalez and center fielder Dexter Fowler collided going for the ball, with Fowler jumping over Gonzalez and getting his glove on the ball but not being able to hold it as he planted a foot in the wall.

De La Rosa had a cut on the middle finger of his pitching hand, which bothered him in his last start. But he checked out fine before the game.

"He struggled through some of his outing and again in the end kept us close enough to win a game," Rockies manager Walt Weiss said of De La Rosa. "He had to work pretty hard, threw a lot of pitches; kept us in striking distance."

Adam Ottavino relieved De La Rosa and gave up a two-out, two-run single to Ian Desmond that gave the Nationals a 4-0 lead. With a single in his previous at-bat, Desmond extended his career-high hitting streak to 14 games.

Held to a bunt single through five innings, the Rockies broke through and scored their only run in the sixth inning when Gonzalez tripled to drive in Jonathan Herrera.

NOTES: Rockies OF Eric Young Jr. was designated for assignment, and RHP Chris Volstad was recalled from Triple-A Colorado Springs and added to the bullpen. The Rockies have 10 days to trade, release or try to put Young through waivers. Volstad pitched the eighth and gave up the Nationals' final run on a pair of doubles. ... Rockies RF Michael Cuddyer did not start for the fifth straight game, but Weiss said he planned to have him in the lineup Thursday afternoon. Cuddyer, who had been bothered by a sore left rib cage, said he was fine, and Weiss said Cuddyer was "feeling much better" but decided to give him one more day and play him in a day game following Wednesday night's game. ... RHP Jonathan Gray, the third overall pick in last week's amateur draft from the University of Oklahoma, signed a contract and will begin his professional career at Grand Junction of the Rookie League. ... RHP Tyler Chatwood will start Saturday against the Philadelphia Phillies. It will be his first outing since June 3, when he left a start after four innings with right triceps soreness. ... Nationals C Wilson Ramos reinjured his left hamstring running first-to-third drills two days ago at the club's facility in Viera, Fla. Johnson termed it a slight setback but said it would be "a long shot" for Ramos to return before the All-Star break. This is the second rehab stint this season for Ramos with his hamstring. He strained the hamstring April 13 and missed 14 games and reinjured it May 15. ... Ohlendorf was brought up from Triple-A Syracuse to start, and RHP Nathan Karns was optioned to Double-A Harrisburg. To make room on the 40-man roster for Ohlendorf, RHP Christian Garcia (right forearm) was transferred to the 60-day disabled list. Karns went 0-1 with a 7.50 ERA in three starts for the Nationals.