Happ left with a 5-1 lead and runners on first and second, but reliever Chad Durbin couldn't hold them on.
Still, it was good enough for the Phillies, who withstood a late comeback by the Nationals. Shane Victorino had four hits, Jimmy Rollins and Carlos Ruiz each doubled twice, leading a 16-hit attack before a sellout crowd of 45,202 at Citizens Bank Park. The Phils improved to 10-14 at home and 26-20 overall.
"I think his [Happ's] confidence level is fine, and it should be fine," Phillies manager Charlie Manuel said. "He's in the rotation."
Happ earned his first win as a starter since Sept. 17, 2008, at Atlanta. He is 2-1 with a 3.69 ERA in seven career starts.
"I felt pretty good about it," Happ said. "I was able to mix it up a little bit more. Obviously, I'd like to go deeper in the game."
Ruiz hit his first double in the second inning, which scored Jayson Werth, tying the game at 1. The Phillies went ahead, 3-1, in the third on a two-run single to right-center by Raul Ibanez, who increased his National League-leading RBI total to 46. Ibanez is also hitting .512 (21-for-41) with 18 RBIs in 10 games against the Nationals this season.
Pedro Feliz added an RBI triple off the wall in center, scoring Ibanez for a 4-1 advantage.
Although the Nationals scored three times in the sixth to get within one run, they could not even the score.
For the Phillies, there was plenty to be optimistic about despite dealing with the loss of Myers.
Victorino, who had his third four-hit game as the Phillies tied a season-high with 16 hits, was tied for first in the NL in hits entering Friday's game.
"He was putting the bat on the ball nice and easy and put it all over the field," Manuel said. "He hit it wherever he wanted to."
With his four hits, Victorino's average climbed from .280 to .293.
"See the ball, hit the ball," Victorino said matter-of-factly. "They fell in. I'm not changing my approach when I'm going up to swing the bat. It is nice to hit line drives that fall in."
Brad Lidge resembled the closer of last year when he was a perfect 41-for-41 in the regular season and 7-for-7 in the postseason as the Phillies won the World Series. Lidge pitched a perfect ninth and struck out Nick Johnson looking to secure his 10th save.
When Johnson struck out, the 18th sellout crowd of the season erupted. With the sellout, the Phillies' total home attendance surpassed one million for the season in the 24th home game, the fastest in Citizens Bank Park history. It last occurred in the 25th game in 2004, the ballpark's inaugural season.
"I felt real good," Lidge said. "I've been feeling better and better. My velocity and location is starting to come back. I'm getting back in that rhythm."
That rhythm especially involves throwing inside with confidence.
"I've been throwing in a lot more and I've also been able to mix up my pitches more," Lidge said.
The result was the 26th win for the Phillies, who have two more games against the struggling Nationals before heading to the West Coast.
"We had 16 hits and left 13 on base," Manuel said. "We could have scored more runs. The 16 hits is an indication that we will score more runs."