PHILADELPHIA — The final, fraying vestiges of the Philadelphia Phillies’ superiority over the Washington Nationals unraveled Tuesday night at Citizens Bank Park. The Phillies sent to the mound Roy Halladay, more obelisk than pitcher, their ace, the right-hander whom the Nationals had never beaten. He proved just as helpless as the rest of his teammates from preventing the sudden reversal of a rivalry.

The Nationals knocked around Halladay in a 5-2 victory even after third baseman Ryan Zimmerman was made a late scratch because of a precautionary manager’s decision. Halladay chucked a rosin bag after he allowed a home run. Bryce Harper, using three years of study and a spring training planning session, drilled a two-run triple off him. The Philles’ catcher was ejected. Halladay’s world, like the recent matchup between Washington and Philadelphia, had been turned upside down.

The Phillies built their five-title reign over the National League East on the Nationals’ backs, but those days ended abruptly. The Nationals have beaten the Phillies in nine of their past 10 games, including four out of five this season and six straight in Philadelphia. Washington leapfrogged the Atlanta Braves into first place — six games clear of the last-place Phillies, the only team in the division with a losing record.

“The Phillies, as far as I’m concerned, are still the king of the mountain,” Nationals Manager Davey Johnson said. “Nobody’s really knocked them off that mountain. My guys know if we want to play with the best, we’ve got to beat these guys. And we’ve been doing a pretty good job.”

The Nationals (26-17) won behind one run over six innings from Jordan Zimmermann, who saved a depleted bullpen by throwing the final nine of his 107 pitches in a 1-2-3 sixth inning. He also added two hits as he earned his first win in five starts against the Phillies. It came against Halladay, who before Tuesday night had gone 9-0 with a 2.13 ERA against the Nationals.

The Nationals smacked nine hits off Halladay in six innings, including home runs by Ian Desmond — who drilled his team-leading eighth — and Rick Ankiel. They attacked him early in the count, not allowing him to dice them with his arsenal of sinkers, cutters, sliders and change-ups, all of which look the same until they dart a few feet in front of the plate. Eight of their nine hits came within the first three pitches of an at-bat, four on the very first pitch.

“Anytime you’re facing a Hall of Fame-caliber pitcher that doesn’t make many mistakes when he pitches, you’ve got to be aggressive,” Johnson said. “He’s going to be hitting the corners and use the whole strike zone. You better be up there swinging.”

In the first three innings, Halladay allowed only two soft singles and struck out two as the Phillies (21-23) took the lead on an RBI ground-rule double by Hector Luna. The Nationals had wrested control of the rivalry, but Halladay would surely take it back.

The third inning stunned the 45,569 at Citizens Bank Park into near silence. Zimmermann ripped the first pitch into left for a single. Steve Lombardozzi lined another hit, bringing Harper to the plate.