WASHINGTON -- Despite the Pirates enjoying the rarity of both Adam and Andy LaRoche contributing on the same night, reliever Tom Gorzelanny stumbled just enough on Thursday to let the Nationals sneak in for the win.

So dominant in the first two games of this series and charged with holding a one-run lead, Gorzelanny gave up two runs in the eighth that eventually proved the difference in the Pirates' 5-4 loss to the Nationals in front of 17,816 at Nationals Park.

The loss snapped Pittsburgh's season-best five-game winning streak and kept the Pirates from successfully completing the team's first four-game sweep on the road in 12 years. Still, it hardly dampened the air of confidence in the clubhouse that has been building with the team having won seven of its past 10 games.

"Tough loss tonight, but we should be pretty pleased with what we accomplished here," manager John Russell said. "We would have loved to have won tonight, but any time you can win three of four on the road, it's definitely a feather in your cap."

"Nobody's hanging their head," Adam LaRoche said. "I think we needed to have something going into Chicago because that's never easy in either of those ballparks. A little momentum now -- hopefully we can carry it out."

The Pirates begin a six-game stay in Chicago on Friday with three games against the White Sox followed by three against the Cubs.

Thursday's game began with Nationals starter Craig Stammen, making his Major League debut, retiring the first 12 hitters he faced before the LaRoches, each finishing with two RBIs, gave the Pirates a 4-3 lead in the seventh.

Gorzelanny, who had recorded key outs in two of the Pirates' first three wins against Washington, followed with a perfect inning of relief in the seventh. Only he couldn't emulate that success in the eighth.

A one-out single in the eighth by Cristian Guzman gave the Nationals an initial spark. A single by first baseman Nick Johnson followed, as did RBI singles by Ryan Zimmerman and Adam Dunn. The latter hit pushed the Nationals back in front, 5-4.

"It was really unfortunate," said Gorzelanny, who picked up a win and a loss in relief during the four-game series. "I felt like I made some good pitches there. That first inning, everything went well. I threw some good pitches. In the eighth inning I threw good pitches, as well, they just got hit."

Gorzelanny remains with the team as a temporary bullpen arm, with Russell saying after the game that no decision has yet been made as to when the lefty will rejoin the Triple-A rotation. Russell hardly seemed soured by Gorzelanny's performance on Thursday.

"I thought he made some good pitches," Russell said. "They didn't hit him really hard. He kept the ball down. His velocity was good. I thought he threw the ball pretty well, just a little tough luck for him."

The blown save by Gorzelanny kept Pirates starter Ian Snell from picking up his second win of the season. Snell fell behind early when Washington pushed across two second-inning runs on a brief rally that began with a leadoff walk.

Nationals outfielder Willie Harris then hit a low line drive down the right-field line that Adam LaRoche was only able to deflect with his glove. A subsequent groundout and sacrifice fly drove in both runs. A two-out single by Nationals catcher Josh Bard in the fourth pushed Washington to an early three-run cushion.

Still, despite an escalating pitch count early, Snell looked sharper as the game progressed. He was removed in the sixth, with the Pirates needing to pinch-hit in his spot, after allowing only four hits, one walk and striking out six. The righty retired eight of the final nine hitters he faced.

"I felt good," said Snell, who remains winless since April 18. "They hit some good, quality pitches. We won the series. That's all that matters."

As Snell settled in, the Pirates chipped away. It wasn't until Adam LaRoche doubled down the right-field line to lead off the fifth that the Pirates put a runner on base. LaRoche eventually scored on a groundout by brother Andy, closing the deficit to 3-1.

Adam LaRoche's double would be the Pirates' only hit until the seventh, when, after a one-out walk to Nate McLouth, he took Stammen deep on a 2-2 pitch to tie the game at 3. Brandon Moss followed with a double and then scored the go-ahead run on Andy LaRoche's single up the middle.

"It's been a blast," the elder LaRoche said of watching his younger brother's recent production. "I'm his biggest cheerleader in there. It's been fun."

Andy LaRoche, owner of a seven-game hitting streak, has hit at a .423 clip over the past week. He's driven in eight in his last 23 at-bats.

Arguably even more remarkable, given their history, is the fact that both LaRoche brothers found success on the same night. They did so in Tuesday's win when each drove in two runs, though both are quick to point out that such an occurrence is quite the uncommon occurrence.

"When I'm doing good, he's not," Andy LaRoche said. "When he's doing good, I'm not. It's been that way even when we weren't on the same team. We've got to figure that out."

Adam LaRoche's 2-for-4 night on Thursday came after he had amassed only one hit in his previous 19 at-bats.