The Colorado Rockies haven't lost since April 30 when Jorge De La Rosa steps foot on the mound.

They will try to keep their ace's unbeaten streak intact Wednesday in the second test of a three-game series versus the Washington Nationals at Coors Field. De La Rosa is 5-0 with a 2.76 earned run average in his last seven starts -- all Colorado victories -- but did not record a decision in a shaky outing Friday versus San Diego.

De La Rosa was reached for 11 hits and four runs in five innings with five strikeouts and no walks for the first time this season.

"I didn't have my best stuff today. They made me work a lot," De La Rosa said of the Padres. "That's why they got those hits against me. When I tried to throw a strike, I left it up, and I paid for it."

He has received a fair share of run support during his unbeaten stretch (43 total) and owns a 7-3 record in 13 starts to go along with a 3.38 ERA. In six home starts this season, De La Rosa is 5-0 with a 3.15 ERA.

The Mexican left-hander has made five career starts against Washington and has produced a 3-1 record with a 4.80 ERA.

Colorado took the opener of this set Tuesday with an 8-3 win. Tyler Colvin hit a pair of two-run homers, Carlos Gonzalez belted a three-run shot during a five-run bottom of the fifth and starter Jhoulys Chacin did enough for the win by allowing two runs in five innings.

"It's one thing to be here, but I know I can contribute to this team and help this team win," said Colvin, who was called up from the minors earlier this month. "Games like tonight justify why I am here."

Gonzalez is batting .250 in his last six games, but has homered four times and driven in 15 runs.

Colorado is just one game behind Arizona for the NL West lead and has won seven of its last 10 games. It is 3-2 on a 10-game homestand.

The Nationals opened their nine-game road trip in losing fashion, as Dan Haren was victimized during a five-run fifth inning on homers by Colvin and Gonzalez and fell to 4-8 on the season. He had an early 2-0 lead, struck out six and walked only one.

"This is a difficult place to pitch, but you have to be careful with the walks and there's a lot of room out there so the ball flys," said Haren. "But it's the same way for both teams so I'm not trying to make any excuses."

Denard Span drove in a pair of runs and Ian Desmond added an RBI for Washington, which had won two straight and three of five games. The Nationals have also dropped nine of the past 11 road contests.

It was confirmed Tuesday that Nationals disabled outfielder Bryce Harper has no structural damage in his balky left knee. Harper visited noted sports surgeon Dr. James Andrews Monday and will be re-evaluated in about a week. He is currently wearing an immobilizer to stable the knee.

"We checked out via MRI his knee and it's structurally sound," Nationals head athletic trainer Lee Kuntz told the club's website. "Everything's good, all the ligaments are intact. No cartilage damage, nothing like that. It's soft tissue in the bursar that's inflamed."

The Nationals' rotation has been banged up as well, forcing the club to recall Ross Ohlendorf from Triple-A Syracuse to make Wednesday's start. Ohlendorf went 4-5 with a 4.27 earned run average in 13 games (12 starts) for the Chiefs and hasn't pitched in the majors since last Aug. 17 with San Diego. In 13 games, nine of which were starts, with the Padres, Ohlendorf compiled a 4-4 mark to go along with a 7.77 ERA.

Ohlendorf, a right-hander, is 1-1 with a 5.00 ERA in six career starts against the Rockies.

The Nationals and Rockies are meeting for the first time this season and are scheduled to clash June 20-23 at Nationals Park. Colorado took four of the seven matchups a season ago.