Jayson Werth is tagged out trying to steal second base in the third inning. (Greg Fiume/Getty Images)

Untouchable here, unparalleled everywhere else, Roy Halladay stood on the Nationals Park mound Monday afternoon and struck an unfamiliar pose. He was looking up and over his shoulder, watching the flight of another one of his pitches scorched toward the seats. Since he joined the Philadelphia Phillies, Halladay had owned the Washington Nationals. Now, as Laynce Nix’s home run stole the lead, they were playing home run derby against him.

The stunning development yielded to an infuriating question by the end of Washington’s 5-4 loss in front of 34,789: What must the Nationals do to beat the Phillies? They had smoked three home runs and smacked 10 hits off the best pitcher on the planet. Livan Hernandez had allowed three runs in 61 / 3 innings when he exited. They did not make an error. And still, the Nationals lost to the Phillies for the sixth straight time, their 33rd defeat against Philadelphia in the past 43 meetings.

The Nationals have lost 10 of their last 12, a stretch that has dropped them to 22-31, the third-worst record in the majors. Twelve of those 31 — including six of the last 10 — have come by one run, the most in the majors. Playing well and coming close, even against Halladay and the first-place Phillies, provides the Nationals scant solace.

“That’s worn off,” second baseman Danny Espinosa said. “We keep losing. It’s just another loss. Play a good game, play a bad game, it doesn’t feel any different. You lose a game, and it still hurts.”

The Nationals, after Michael Morse, Espinosa and Nix drilled solo homers off Halladay, lost the game with their bullpen. Sean Burnett replaced Hernandez with one out in the seventh inning, the Nationals up 4-3 and a runner on first. Burnett had held left-handed batters to a .179 average this year, and Manager Jim Riggleman called on him with three lefties coming up: Chase Utley, Ryan Howard and Raul Ibanez.

Burnett began Utley with two strikes before Utley displayed what makes him one of baseball’s toughest outs. In the next six pitches, Utley fouled off two and took four balls, drawing an eight-pitch walk.

“On 3-2,” Burnett said, “you got to make him hit the ball.”

Howard came to the plate, and with a 1-0, 93-mph sinker, Burnett induced a chopper to the right side. Somehow, it snuck between Morse and Espinosa. Placido Polanco raced home with the tying run and Utley scooted to third. Ibanez, who entered with a 1.037 OPS against the Nats, smoked a sacrifice fly to right that gave the Phillies a 5-4 lead.

“Just flat out terrible,” Burnett said.

The Nationals created one excellent chance to tie the game, and, as is their recent custom, they found the most frustrating way to squander it. Alex Cora led off the seventh with a bloop double to right. Ian Desmond followed with a bunt single, the Nationals’ 10th hit off Halladay — four less than they had produced in 25 prior innings against him at Nationals Park.

With no outs and runners at the corners, Rick Ankiel ripped a groundball up the middle. Halladay knocked it down between his legs. On third, Cora sprinted home on contact — if he didn’t run, he would risk the Phillies turning a double play and leaving one runner on with two outs.

“There’s nothing I could do,” Cora said. “As soon as he hit it, I was gone.”

Halladay scooped the ball and fired home, and Cora was out in a rundown. When Espinosa followed with a fly to right field, it was simply the second out — not a game-tying sacrifice fly. And when Jayson Werth struck out, the inning ended.

Of the many possibilities on a 95-degree day, Teddy Roosevelt winning the Presidents Race ranked as more likely than the Nationals tattooing Halladay. (Teddy lost, too.) In three starts at Nationals Park, the 2010 Cy Young winner had allowed the Nats three earned runs, striking out 24.

When Morse walked to the plate to lead off the second, Halladay had not allowed a home run to the Nationals in 142 at-bats. And then Morse rocked a 1-2 two-seamer to the red seats in left-center, his fifth home run in seven games. The Nationals made their lead 2-0 once Hernandez bunted home Jerry Hairston with a clinical safety squeeze.

Hernandez cruised through three innings, but these were still the Phillies. Five consecutive Phillies reached base against Hernandez in the fourth, including back-to-back homers by Howard and Ibanez, a furious stretch that gave the Philles a 3-2 lead.

Usually, a one-run lead for Halladay would count as insurmountable. Not Monday. Espinosa came up in the fifth two outs, the bases empty. Halladay struck out Espinosa in their first two meetings.

“I don’t feel that it’s ever a truly comfortable at-bat against him,” Espinosa said. “He might give you one pitch an at-bat, and you need to take advantage of it.”

In the fifth, Espinosa worked the count to 2-2, and Halladay made that rare mistake. He left a change-up down and in. Espinosa sent a deep drive to right field, into the second row of seats on top of the scoreboard to tie the game.

When Nix smashed a leadoff homer in the sixth, scalding a 91-mph four-seam fastball, the Nationals had stunned Halladay and taken the lead. The Nationals’ assault on Halladay staggered him, but it only served to provide a more interesting path to a typical end.