Jayson Werth walks off the field after hitting into a double play to end Saturday’s 2-1 loss to the Rockies. (Rob Carr/Getty Images)

Following more than month when they accumulated wins en masse by a single run or in extra innings, the Washington Nationals absorbed their third straight loss by the narrowest of margins, 2-1 against the Colorado Rockies on Saturday night.

The 29,441 in attendance at Nationals Park let the team hear about it too, booing heartily after right fielder Jayson Werth, awarded the most lucrative free agent contract in team history during the offseason, grounded into a double play with runners at the corners to end the game.

Washington (45-46) now must win the final game of this three-game series to be assured of a .500 record at the all-star break. Just three days ago, after winning its third straight and with all 10 victories since June 21 by a run or in extra innings, that prospect hardly seemed in doubt.

“Right now we’re living and dying by the one-run game,” shortstop Ian Desmond said. “It’s going to get going though. We’re playing good defense. Our pitching is great. These one-run games are just flukes, just one of those things. It’ll turn around for us.”

Desmond was one of just two Nationals players to collect multiple hits off Rockies starter Ubaldo Jimenez, who went eight innings and allowed one run on five hits with eight strikeouts. The Nationals, meanwhile, wasted another quality start from Jason Marquis, who yielded two runs in six innings in another hard-luck loss.

On Saturday, the right-hander combated control issues but largely managed to keep pace early on with the at-times overpowering Jimenez, who entered 3-0 with a 1.53 ERA and 21 strikeouts in his last three starts against Washington.

But Marquis began the fourth by yielding a home run to slugging first baseman Todd Helton that landed roughly a half-dozen rows deep in left center. Helton’s 10th this season came on a 2-2 slider that never broke, instead sitting up over the heart of the plate. It was just the second flyball Marquis had permitted over the first three-plus innings.

Back in the lineup after missing four games with a strained right quadriceps, all-star shortstop Troy Tulowitzki followed with a single to left, and after Marquis got Seth Smith to pop up and Ty Wigginton to ground out, Ian Stewart drew a walk. Chris Iannetta walked one batter later to load the bases.

Fortunately for Marquis, Jimenez was next to the plate, although the ensuing groundball out was far from routine. Third baseman Ryan Zimmerman had to charge the ball on a soft roller and come up throwing to get the runner.

Marquis courted trouble to start the fifth too, surrendering a leadoff single to Ryan Spilborghs and immediately thereafter a double to Mark Ellis that rolled deep into the left field corner. With Spilborghs attempting to score on the hit, Laynce Nix quickly delivered a strike to cutoff man Desmond, who fired home.

Making his first big league start in more than two years, catcher Jesus Flores had the ball in his glove well ahead of the sliding Spilbroghs, and when home plate umpire Jerry Layne signaled out on the tag, the Nationals had to contend with only Ellis standing on third. Running on the pitch, Ellis scored moments later when Helton grounded softly to first base and Michael Morse had no reasonable play at home.

Marquis got Tulowitzki to fly out to center for the last out of the fifth, and the Nationals had the makings of at least a somewhat lucrative home half when Morse singled and Jayson Werth walked with one out. The threat ended, though, with Flores, called up on Friday when Ivan Rodriguez went to the 15-day disabled list, grounding into a 6-4-3 double play.

After working a perfect sixth, Marquis’s evening was done when Rich Ankiel pinch-hit for him in the bottom of the inning. The Nationals then turned to Ross Detwiler to keep them in the game, and the spot starter/middle reliever obliged. Recently called up for a last-minute start, Detwiler gave up a single hit over two innings before Todd Coffey worked a perfect ninth.

The Nationals, meantime, finally were able to get to Jimenez a bit in the eighth. That’s when Desmond singled and Roger Bernadina did the same to put the go-ahead runs on base with two outs. Danny Espinosa stepped to the plate, and fans began chanting his first name throughout the stadium in anticipation of perhaps the second baseman adding to his team-high 16 home runs.

The rookie of the year candidate had several solid cuts, but Jimenez worked out of the predicament by inducing a flyball to left that sailed high before harmlessly settling into Wigginton’s glove.

In the ninth, Zimmerman led off against closer Huston Street beating out a single that Tulowitzki had trouble fielding cleanly, and after Nix struck out, Morse singled to move Zimmerman to third. That set up Werth’s at-bat, which ended meekly and ensured the Nationals would lose their first series of this season-long 11-game homestand that concludes on Sunday.

“When games are tight like that, sometimes they go your way, sometimes they don’t,” Espinosa said. “You just go out there, and you’ve got to play as hard as you can and give yourself the best opportunities, and hopefully the game goes your way.”