DENVER(AP) Waiting out Jorge De La Rosa 's early season struggles has allowed the young Rockies left-hander to play a central role in Colorado's mid-season surge.

De La Rosa pitched effectively into the seventh inning to earn his career-best fourth straight win, Ryan Spilborghs hit a bases-loaded triple to key a four-run fifth and the Rockies beat the Washington Nationals 10-4 Wednesday to complete a three-game sweep.

Troy Tulowitzki hit a two-run homer among his three hits and Carlos Gonzalez added three more hits for the Rockies, who have beaten the Nationals six straight times since August.

Colorado's third sweep in its last five home series put the Rockies six games over .500 for the first time this season. They have gone 30-15 (.666) since May 21, the best winning percentage in the majors.

De La Rosa (6-7) has been a key part of the Rockies' resurgent play, winning six of his last seven starts after going 0-6 with four no decisions in his first 10. Manager Jim Tracy said the Rockies' determination to keep him in the rotation could prove to be one of the season's pivotal decisions.

''When you're trying to develop, patience is a key word,'' Tracy said. ''You talk about Jorge or another young guy like Carlos Gonzalez , if they're going to get it, the only way they're going to get it, is to go out there and do it. When you get to the point where you can no longer do that any more, then it becomes time to make another decision, but we had not reached that point and Jorge turned the corner. It could end up over the course of the second half of the season being a very profitable decision.''

De La Rosa credited improvements in his two-seam fastball and control, along with an unwavering belief in himself, for the turnaround.

''I never lost my confidence,'' he said. ''I always believed in myself. I'm throwing better. I'm throwing more first pitch strikes. I have much better command.''

Washington manager Manny Acta said De La Rosa made it tough on Nationals hitters.

''He has quite an arsenal of pitches and can be tough when he's throwing strikes,'' Acta said. ''Today he was throwing strikes.''

De La Rosa shut down the Nationals until tiring in the seventh inning. He struck out Ryan Zimmerman to start the inning but then walked Adam Dunn and Austin Kearns around Josh Willingham 's single to load the bases and was lifted after 6 1-3 innings.

Josh Fogg relieved and Anderson Hernandez greeted him with a two-run single. Will Nieves followed with a sacrifice fly as the Nationals avoided being shut out for the second time in the series.

De La Rosa gave up three runs and five hits with five strikeouts and three walks.

''Any time his walks are down, he ends up pitching a good game,'' added Tulowitzki. ''He has some of the best stuff I've seen from a lefty. Any time you pitch 94, 95 mph with a good changeup, you're going to be tough to hit. So as long as he challenges the strike zone, he gives us a chance to win.''

The Rockies built a 2-0 lead on run-scoring doubles by Todd Helton and Dexter Fowler before taking control with a four-run fifth inning.

Rookie Ross Detwiler (0-5), who allowed six runs on eight hits in four innings, gave up successive singles to Helton and Garrett Atkins and walked Tulowitzki to load the bases. Spilborghs followed with a triple to left field, clearing the bases and chasing Detwiler, the Nationals' top selection in the June 2007 draft who is still seeking his first big league win.

''I was getting ahead of some people and didn't finish them off. I left some pitches up and they got hit,'' Detwiler said.

NOTES: Zimmerman was credited with an additional base hit in Tuesday night's 5-4 loss to Colorado after the official scorer reversed his decision charging Tulowitzki with an error on a seventh-inning play ... LHP Matt Chico , in the midst of a comeback from Tommy John surgery, was reinstated from the disabled list by the Nationals and then optioned to Double-A Harrisburg. ... Helton is five doubles shy of becoming the 49th player with 500. ... RF Spilborghs registered his team-high sixth outfield assist when he threw out Nyjer Morgan at third base as the Nationals' leadoff man tried to advance on Alberto Gonzalez 's first-inning single. ... The Rockies have six series sweeps overall this season.