WASHINGTON -- Ryan Zimmerman loves the big moments.

He wants to be the one at the plate with the game on the line. He wants to be the one to carry his team to a victory. And on Saturday, he proved it.

Zimmerman's walk-off three-run homer off Brad Lidge blasted the Nationals over the Phillies, 7-5, on Saturday night in front of 38,049 at Nationals Park.

Since he debuted in Washington on Sept. 1, 2005, Zimmerman leads the Major Leagues with seven walk-off home runs. Yet he couldn't explain why he is so successful in the pressure-packed situations.

"I wish I could tell you," Zimmerman said. "I just treat it like any other at-bat, and try to think that the pressure is on him and not on me. Just put a good swing on it, not do too much."

The Nationals are now 46-58 on the season and have won four of their past five games. Reliever Drew Storen (3-2) got the win after finishing out the top of the ninth.

And even trailing 5-4 in the bottom of the frame, the Nationals did not back down.

Michael Morse began with a single to center field off Lidge. Nyjer Morgan then laid down a sacrifice bunt and Adam Kennedy followed with a walk to put runners on first and second. Zimmerman took a 2-1 fastball from Lidge over the center-field fence to finish the job.

"I went with a fastball in," Lidge said. "I actually shook to get the fastball in on Zimmerman, which is a pitch I've had a lot of success against him with. I went back and looked where the pitch was. It was on the inner third, but he was ready for it tonight."

"There are certain guys that seem to step up in those clutch situations," Storen said. "Obviously, as a fan, before I even signed, I knew that he was a guy that did that. It's something that's pretty awesome and great to have, especially as a late-inning reliever."

But getting to that point wasn't easy. The usually-reliable Washington bullpen, which had not allowed a run in its past 14 1/3 innings, nearly fell apart.

Joel Peralta entered the game in the sixth inning with one out, but he promptly gave up a solo home to Carlos Ruiz to put the Phillies within two runs.

Tyler Clippard replaced Peralta in the seventh with the Nationals leading, 4-2. But on the third batter of the inning, he surrendered a two-run home run to Raul Ibanez that tied the game at 4.

In the ninth, with the game still tied, Sean Burnett issued a leadoff walk to Jayson Werth, who moved to third with two outs. Storen replaced Burnett and gave up an RBI single to Ruiz.

"That's what happens when you face a good hitter like that," Storen said. "I thought I was going to be able to elevate a fastball past him there and he just got the barrel on it. Obviously, I owe 'Zim' at least a dinner."

The poor pitching late in the game almost wasted a strong start by left-hander Ross Detwiler.

Coming off a subpar first game of the season -- he was rehabbing from hip surgery -- Detwiler bounced back with sharp outing against the Phillies. He allowed one run on five hits in 5 1/3 innings, with the only blemish coming on Wilson Valdez's RBI single in the fourth inning.

"It's a stepping stone," Detwiler said. "It's definitely not where I want to be, but the team stayed in the game and we ended up winning. It's a good stepping stone."

The Nationals took two of three games against the Braves earlier this week. Now, they have a chance to sweep the Phillies.

Adam Dunn said the team's recent success shows that it's moving in the right direction.

"We put ourselves in a position to be where we need to be," Dunn said. "As far as sweeping [the Phillies], we have already done a great job of taking the series. Hopefully, tomorrow we will put it together and keep it rolling."