The victory, accomplished Monday night against the skidding Nationals, was meaningless in comparison to the ramifications that could come from a ninth-inning pitch thrown by All-Star closer Jason Grilli.
After the pitch, the right-hander left with forearm tightness -- leaving his manager and teammates somberly hoping for the best.
"It's never good to see somebody in pain, let alone your All-Star closer," starting pitcher Charlie Morton said.
Grilli entered in the ninth and gave up a two-run homer to Jayson Werth before leaving with an apparent arm injury after getting two outs.
"Pretty much he threw the ball, and his reaction was, he just grimaced a little bit," Pirates catcher Russell Martin said. "It seemed like he was in a little bit of pain. It just looked like his forearm was bugging him. A definite blow. Hopefully it's not as severe as it can be and is just something minor."
Grilli was not made available to the media after the game.
Manager Clint Hurdle tried to remain upbeat, saying, "We'll wait and see where Grilli's situation goes. Right now it's right forearm discomfort. We're going to wait and see how he feels (Tuesday)."
Asked what the Pirates would do if Grilli was lost for an extended period, Hurdle snapped, "And what if he's not? Our roster is going to be fine."
It was a disappointing ending to a night that started so well.
McCutchen connected in the first inning and again in the third to stake the Pirates to a 4-0 lead. The All-Star center fielder has five homers in his last six games and 14 for the season.
Both homers came off Dan Haren (4-11), who's 0-8 in 11 starts since May 9.
McCutchen is 18 for 35 with five homers and 12 RBIs in his last nine games at Nationals Park.
"Every player always has a ballpark he seems to hit at better than other places," he said. "I guess mine happens to be here."
Although he went hitless in his final three at-bats, McCutchen is hitting .431 with 13 home runs and 26 RBIs in 27 career games against Washington.
Morton (2-2) gave up three runs, six hits and a walk in 6 2/3 innings to earn his first win in five starts. He was lifted after yielding a two-run homer to Werth.
"When you get later in the game, especially if you're pitching well -- which I was -- you like to finish off the outing on a strong note," Morton said. "Giving up a two-run homer isn't exactly what you want."
Werth's two homers gave him four in two games. Adam LaRoche also connected for the Nationals, who have lost four straight and nine of 11 to fall three games under .500 (48-51) for the first time this season.
"There's a lot of character on this ballclub, there's no quit, there's a lot of fight," manager Davey Johnson said. "By and large everybody swung the bat pretty good."
Before the game, general manager Mike Rizzo fired hitting coach Rick Eckstein in an effort to shake up a lackluster offense that ranked 27th in batting average and tied for 28th in runs scored.
The Nationals failed to get the ball out of the infield until the fifth inning, hit into three double plays and went 0 for 3 with runners in scoring position.
But at least they scored five runs, which matched their total for the previous three games.
"That's really the first time we've had something going in a while," Werth said. "It was a good feeling. Hopefully we can get the job done next time and build on that."
Eckstein's replacement, Rick Schu, is expected to join the team Tuesday.
The Pirates took the lead for good after three batters went to the plate. Jordy Mercer drew a one-out walk and McCutchen followed with a drive into the right-field bleachers.
LaRoche's 14th home run leading off the fifth was Washington's first hit, and Werth connected with LaRoche at first base with a man on in the seventh.
Pittsburgh made it 6-3 in the eighth, scoring a run on a wild pitch by Drew Storen.
Pirates 2B Neil Walker (strained oblique) joined the team Monday after playing three games with Triple-A Indianapolis. Hurdle said Walker will be activated off the disabled list on Tuesday "If he shows us he's good to move around." ... Nationals starting pitchers have one win in the last 11 games. ... Pittsburgh's Clint Barmes played in his 1,000th career game. ... The Pirates have eight homers in their last four games. ... Pittsburgh went 0 for 10 with runners in scoring position.