WASHINGTON -- The Philadelphia Phillies are the NL East champions for the fourth consecutive year and, fittingly, Roy Halladay helped seal the deal this time with a two-hitter.

Halladay earned his 21st win with his fourth shutout and ninth complete game -- all highs in the majors this season -- and Jayson Werth drove in four runs, leading the Phillies to a 8-0 victory over the Washington Nationals on Monday night, wrapping up the division with five games left.

Halladay (21-10) heads to the playoffs for the first time in his 13th major league season, having played his entire career with the Toronto Blue Jays before being traded to Philadelphia last winter.

Normally stoic on the mound, the former Cy Young winner punched his glove with his pitching hand after striking out a swinging Danny Espinosa for the final out.

Halladay instantly broke into a big smile, and the Phillies gathered in the middle of the diamond for hugs and high-fives. Thousands of red-clad, towel-waving Phillies fans in the announced crowd of 14,309 gave a standing ovation then began their last in a series of "Let's go, Phillies" cheers.

And Halladay was in the middle of the celebration. His years without a postseason trip were tied for fourth-most among active players; the highest total on that list belongs to Mike Sweeney, a bench player whose drought ends in his 16th season.

"It was fun, but it's only going to get funner," Halladay said. "Honestly, it didn't matter who finished it as long as we got it done."

Halladay then joined his teammates in a soaked clubhouse for the victory party. The Phillies have the best record in the NL -- it's still uncertain who they'll face at home next week in Game 1 of the division series.

Completely undisturbed by a light rain that began falling in the third inning, Halladay gave up a single to Wilson Ramos in the third, and another to Adam Dunn in the eighth. But that was it.

The right-hander didn't walk a batter and struck out six, including one to end each of the first three innings. He faced the minimum 21 batters through seven innings, because Ramos was erased when the next hitter, Alberto Gonzalez, grounded into a 4-6-3 double play.

The Phillies went ahead 1-0 on the first of Werth's three hits in the game. It was his 26th homer, a drive to left field off John Lannan (8-8) in the second inning.

Because of Halladay's dominance, that would have been enough to win on this night. But Werth made it 3-0 in the sixth, delivering a two-out, two-run double to right-center after Lannan walked Placido Polanco and hit Chase Utley with a pitch. Carlos Ruiz's RBI double later in the inning, off Craig Stammen, drove in Werth and stretched the lead to 4-0.

Lannan, in his final start of the season for the last-place Nationals, gave up four runs and seven hits in 5 2-3 innings.

Werth also brought home a run with an infield single off reliever Miguel Batista in a four-run ninth that included Polanco's RBI single and Utley's two-run double.

Each hit for Philadelphia led to raucous cheers that must have made it feel like a home game for the Phillies. About 35 minutes before the first pitch, a loud roar greeted Halladay as he walked toward the visitors' bullpen beyond left field, wearing a red warmup jacket to brace against the chill of temperature in the 70s.

The first loud yell of "Let's go, Phillies!" was heard not much later. And full-throated choruses of that line reverberated through Nationals Park in the sixth inning.

Plus, when the Phillies were dressing for the game, they found plastic sheets rolled up and tied with string set up above the wooden locker stalls in the visiting clubhouse, preparation for the beverage-spraying celebration.

Might as well have been Citizens Bank Park -- except a lot emptier in the stands.

The only moment when Halladay appeared ruffled in the least bit was in the ninth inning -- when he was at the plate. Nationals reliever Joe Bisenius threw a pitch that made Halladay duck and tumble in the batter's box, mussing his jersey with dirt. That prompted an expletive-filled chant from Phillies supporters.

An inning earlier, reliever Collin Balester sailed a curveball over Werth's head, and home plate umpire Todd Tichenor issued a warning about throwing at batters, which drew Nationals manager Jim Riggleman out of the dugout for a brief conversation.

Nothing was going to slow the Phillies on Monday, though, and they improved to 46-17 since July 21, when they trailed Atlanta by seven games. Eight days later, they traded for Roy Oswalt, adding him to Halladay and 2008 World Series MVP Cole Hamels for as fearsome a threesome of starting pitchers in the majors.

And what a stretch run: Philadelphia is 20-5 in September, its most wins in the season's final month since compiling 22 in 1983.

Looking to become the first team in 66 years to win three consecutive National League championships, the Phillies started this season strong, before injuries and an inconsistent offense took a toll. Six of Philadelphia's eight regulars spent time on the disabled list, and nearly all saw their production decline. At one point, Utley, Ryan Howard and Shane Victorino were absent during a nearly two-week stretch in August.

Unlike previous years, when they counted on a potent offense, the Phillies relied on outstanding pitching in 2010. Led by Halladay, Hamels and Oswalt, the starting rotation dominated, especially in September. Still, it was a much tougher road to the postseason than a year ago, when Philadelphia moved into first place for good on May 30, before eventually losing to the New York Yankees in the World Series.

But the Phillies have done this late-season chase successfully before -- and wrapped things up against the Nationals before. In 2007, the Phillies trailed the Mets by seven games with 17 remaining. Taking advantage of New York's historic collapse, Philadelphia clinched the division on the final day of the regular season by beating Washington, ending a 14-year postseason drought.

In 2008, the Phillies were 3 1/2 games behind the Mets with 17 to play in '08. Philadelphia again caught New York in the final week, clinching the NL East on the next-to-last day of the regular season with a victory against Washington. Philadelphia went on to capture its second World Series title.

NOTES: Philadelphia SS Jimmy Rollins did not start the game because rain much of Monday left the outfield grass slick. Rollins pinch-hit on Sunday after sitting out 14 games with a tight right hamstring. "The weather is why I didn't play him. I figured the field's going to be wet," manager Charlie Manuel said. "What do I gain by playing him?" ... Nationals 3B Ryan Zimmerman probably will miss the rest of the season because of an injured rib muscle on his right side that's sidelined him since last week. ... The Nationals announced 1B Tyler Moore is their minor league player of the year, and LHP Tom Milone is their minor league pitcher of the year. Moore hit .269 with 43 doubles, 31 homers and 111 RBIs at Single-A Potomac; Milone went 12-5 with a 2.85 ERA and 155 strikeouts in 27 starts at Double-A Harrisburg.