But once Sean Burnett came on for the eighth, he promptly allowed a home run to pinch-hitter Eric Young before allowing singles to the next two batters, Dexter Fowler and Marco Scutaro. Young went 481 at-bats since his last homer, which came on Sept. 8, 2009.
With runners on the corners, Michael Gonzalez entered from the bullpen. Facing Carlos Gonzalez, the lefty reliever bounced his fifth pitch into the ground, allowing Fowler to score from third. Charged with the wild pitch, Gonzalez recovered to strike out the next three Rockies.
"It just wasn't my day," Burnett said. "It was supposed to be a sinker to Young and it just cut, I think I pulled it right middle-in. He didn't miss it."
In the ninth, Tyler Clippard entered with a 19 1/3-inning scoreless streak dating back to May 18. But after Jordan Pacheco ripped Clippard's first pitch to left field for a double, Jonathan Herrera bunted Pacheco over to third before Clippard threw a changeup into the backstop. Pacheco scored, giving the Rockies the lead for good.
"I pulled the changeup," Clippard said of his wild pitch. "Can't remember the last time I threw a wild pitch, so it's kind of frustrating to do it in that situation. So what are you going to do?"
Desmond led off the ninth with a single off Rockies closer Rafael Betancourt and was bunted over to second by Danny Espinosa. Two batters later, Roger Bernadina walked, giving the Nationals runners on first and second with two outs. Jesus Flores came on to pinch-hit for Tyler Clippard. On Betancourt's first pitch to Flores, Desmond and Bernadina executed a double steal to put themselves in scoring position. But three pitches later, Flores struck out to end the game.
The loss gave the Rockies the series win, marking the first the Nationals have lost a series since June 22-24 against the Orioles. The Nats also split a four-game set June 25-28 in Colorado.
"We beat a very good ballclub today, the team with the second-best record in baseball," Rockies manager Jim Tracy said. "We feel awfully good about the way we gutted that thing out today."
A silver lining for the Nats came from Desmond, who blasted his 17th home run of the season in the fourth inning, already a career high. The two-run blast followed an Adam LaRoche double, giving Desmond 51 RBIs on the year. That RBI total, as well his .515 slugging percentage lead all NL shortstops.
"Great first half," said Desmond, who will sit out the All-Star Game due to lingering oblique issues. "Most importantly, we're in first place. That's really the only thing I care about. ... I'm just happy that we're in first place and I'm contributing."
The Nats added another run in the seventh, when Bernadina -- pinch-hitting for Zimmermann -- walked with two outs. After stealing second, Bernadina scored on a RBI single by Steve Lombardozzi. However, Lombardozzi was caught in a rundown between first and second, ending the inning.
The Nats enter the All-Star break with the NL's best record at 49-34. Their .590 winning percentage falls just shy of the 2005 Nationals' .591 (52-36) first-half mark in the franchise's inaugural season in Washington.
"We've been playing good all year, a lot of guys have stepped up," Clippard said. "I don't think anybody really thought or knew what kind of club we were. We had a lot of new faces. We knew we had a lot of talent, but I think we're all satisfied by where we're at right now."