A slow start and one swing prevented Gio Gonzalez from becoming the first 17-game winner in the majors.

Philadelphia scored two runs in the opening inning and John Mayberry Jr. hit a tiebreaking homer off the Nationals lefty leading off the sixth as Washington lost its third in a row, 4-2, to Roy Halladay and the Phillies on Saturday night.

Gonzalez (16-7), a former Phillies farmhand, lasted six innings and gave up five hits while striking out seven and walking two. Mayberry's homer was the only hit allowed by Gonzalez after the second.

"I tried to be too careful in the first inning," Gonzalez said. "I got more aggressive."

Steve Lombardozzi drove in both runs for short-handed Washington, which had seven hits while playing without injured starters Ian Desmond (hamstring) and Michael Morse (hand).

"Our offense is struggling a little with (injured players) out, but you've got to give credit to their pitching," Nationals manager Davey Johnson said. "That's not chopped liver over there. They've got a lot of talent."

Gonzalez had baffled the Phillies in two previous starts this season, going 2-0 with a 0.69 ERA and 16 strikeouts in 13 innings. But the Phillies jumped on Gonzalez right away this time.

"Gio's tough," Philadelphia's Chase Utley said. "There are not a lot of lefties that have his velocity. He's definitely commanding the ball a lot better than he has in the past and his numbers show that. You try to get strikes in the strike zone and try not to miss them. We scored some early runs, which is always nice for the starting pitcher."

Philadelphia grabbed a 2-0 lead in the first on RBI singles by Utley and Mayberry. Gonzalez needed 31 pitches to get through the opening frame.

"Gio had a little trouble early but then he settled down," Johnson said.

Mayberry hit a leadoff drive in the sixth inning to give the Phillies a 3-2 lead. It was just the eighth homer allowed this season by Gonzalez, who had yielded one in his last six starts.

"It was a first-pitch fastball," Gonzalez said. "I left it up and he hit it over the wall. "These guys can swing the bats and they know how to work the count."

Mayberry's sacrifice fly in the eighth scored Utley, who stole second and third after being hit by a pitch.

Halladay and the Phillies seem to have their groove back.

"We've got a little step in our get-a-long," manager Charlie Manuel said after the Phillies own their second straight over the NL-East leading Nationals.

Halladay (8-7) allowed two runs and seven hits, struck out six and walked one in seven innings. The right-hander, who missed 42 games with a strained muscle, is 4-1 with a 2.75 ERA in his last five starts.

"I didn't have to force as much today," Halladay said. "From fifth inning on, it's probably the most consistent it's been in a while. I felt pretty good today. I felt like I wasn't laboring as much and that makes a difference."

The two-time Cy Young Award winner improved to 12-2 in 17 career starts against the Nationals franchise while Philadelphia won for the sixth time in the last eight games.

"It feels good to play well," Halladay said. "We've done that at times this year. We want to get back to playing the way people have come to expect of the Phillies."

After Antonio Bastardo struck out the side in the eighth, Jonathan Papelbon pitched a scoreless ninth for his 29th save in 32 chances. The three Phillies pitchers combined for 11 strikeouts.

The five-time defending NL East champion Phillies are seven games under .500.

"Obviously you want to play great baseball all year long," Utley said. "Right now we're playing good baseball, but there's still room for improvement."

The Nationals tied it in the fifth inning on Lombardozzi's two-out, two-run single to center. Washington loaded the bases with one out on three straight singles, but had Gonzalez batting. After two failed bunt attempts, Gonzalez grounded sharply to Utley at second. Instead of trying for the double play, Utley came home to get the lead runner.

Lombardozzi then singled to center to score Danny Espinosa and Kurt Suzuki, who just beat the throw by getting his hand on the plate and under the tag of catcher Erik Kratz.

Morse did not play after leaving Friday night's game with a bruised right hand after he was hit by a Kyle Kendrick pitch in the first inning. Desmond also missed his second straight game due to a right hamstring strain.

NOTES: Phillies OF Domonic Brown was out of the starting lineup due to right knee soreness. It was the first time Brown did not start since being recalled from Triple-A Lehigh Valley on July 31. Brown hit for Halladay in the seventh inning and struck out. ... Philadelphia LHP Cliff Lee (2-7, 3.78 ERA) is scheduled to face RHP Jordan Zimmermann (9-7, 2.54 ERA) in Sunday's series finale.