Phillies shortstop Jimmy Rollins is congratulated after an inside-the-park home run in the fourth inning. (Ricky Carioti/The Washington Post)

The Philadelphia Phillies shambled into Nationals Park on Tuesday night, recognizable only by the laundry on their backs, the remnants of what they used to be. They had spent the afternoon dismantling their team and raising the white flag on a lost year. They no longer bullied or even threatened the Washington Nationals. The Phillies are relegated to the same, unsatisfying role the Nationals once filled: spoiler.

The Phillies are done, but as their 8-0 defeat of the Nationals can attest, they can still be dangerous. The Nationals returned home after winning six of seven games on the road, the best record in the major leagues in their back pocket and their ace on the mound. Then they crashed against the rival they have surpassed as Stephen Strasburg, six days after one of his finest performances, struggled to perhaps the worst start of his career.

Strasburg allowed six runs in only four innings and seemed shockingly vulnerable. A journeyman named Kevin Frandsen crushed a two-run, opposite-field home run, his first major league homer since 2007. Phillies starter Cliff Lee singled and stole a base against him. Jimmy Rollins ripped an inside-the-park home run. Strasburg’s night ended after he batted for himself in the fourth inning, having yielded eight hits and thrown 65 pitches.

Strasburg lacked his best stuff and location. “I think I threw one fastball down the way I wanted to — the first pitch of the game,” Strasburg said. “Other than that, everything was up.”

But his mental approach suffered, too. As the Phillies jumped on him, Strasburg let frustration change his approach. Rather than relying on easy, precise fastballs — as he did when he struck out 11 over seven shutout innings last Wednesday — Strasburg tried to make perfect pitches.

“It’s just a long grind and you can’t be totally dominant every time you go out there,” Manager Davey Johnson said. “He expects it of himself. He makes a bad pitch, and the guy hits it out of the ballpark, it makes him try harder. . . . When he’s not hitting spots and not missing bats, he loses a little bit of his cool demeanor.”

Only once in his career had Strasburg allowed more than four earned runs. He had failed to make it out of the fourth only once, not counting starts he made last year as he essentially rehabbed in the majors.

“When you’re always falling behind, you’ve got to really fight yourself, and just keep on trying to pitch and let it happen,” Strasburg said. “I had a tough time trying to get back in that groove tonight.”

The Nationals slogged to one of their uglier losses without Ryan Zimmerman and Adam LaRoche, both sitting out with apparently minor back problems. Both are expected to return Wednesday, but Tuesday the Nationals used Mark DeRosa and Tyler Moore as their corner infielders. Lee shut down the Nationals’ diminished lineup, allowing five hits and one walk over seven scoreless innings for his second win of the season.

Before Tuesday, the Nationals had in effect lapped the Phillies twice over. The Nationals stood above them in the division by 16½ games. The Phillies, at 45-57, shipped outfielders Shane Victorino and Hunter Pence to the Los Angeles Dodgers and San Francisco Giants, respectively, an official admission that their reign had ended.

“Once you do that, there’s not expectations on them,” Johnson said of the Phillies. “They’re free-wheeling it.”

They can still have their nights. With Strasburg faltering, Johnson could at least conserve innings for later in the season, when the Nationals will shut him down upon reaching a yet-to-be-determined limit.

“Obviously, he was fighting it,” Johnson said. “It was time to shut it down.”

The Nationals put the restrictions on Strasburg in his first season after Tommy John surgery. Pitchers returning from ligament-replacement surgery typically encounter inconsistency. Tuesday, he left his fastballs over the plate and could not entice the Phillies with his breaking pitches, but he rejected the notion that his health history played any role.

“I’m not blaming it on having Tommy John,” Strasburg said. “It happens to everybody. I’m just going to forget about it and make the adjustments. It has nothing to do with coming off of Tommy John. That’s over two years now.”

Strasburg’s troubles began in the second inning. Carlos Ruiz ripped a double to right field to lead off the inning. Strasburg struck out Laynce Nix and John Mayberry, flailing at offspeed pitches. With two outs and Strasburg almost out of the inning, Frandsen ambushed him. He roped a first-pitch, 95-mph fastball over the right-center field wall, giving the Phillies a 2-0 lead.

“He’s been always an emotional guy,” catcher Jesus Flores said of his pitcher. “After the homer, he kind of started forcing himself to make perfect pitches. It seems like it didn’t work out.”

The Phillies added another run in the third, when Juan Pierre scored of his own volition. He smacked a single up the middle. He stole second when Strasburg lost track of him. Not satisfied, Pierre stole third. Flores rushed and fired the throw into left field, allowing Pierre to scoot home.

“I’m pretty upset with myself for letting guys steal on me like that,” Strasburg said. “That’s something where if things aren’t going right, you still have to remember that there’s guys on base. You got keep them close.”

Enough Phillies faces have remained the same that it came to resemble a Nationals-Phillies game from the Nationals’ dark ages. In the fourth, Mayberry smashed a 97-mph fastball off the left field wall. Lee singled him home with two outs. Rollins followed with a line drive to right field that proved the night had come fully unraveled.

As Rollins raced to first, Bryce Harper sprinted back to the right field fence. He crashed off the wall and tumbled, head over heels, as the ball bounded back toward the infield. Rollins wheeled around the bases as Harper gathered himself. Center fielder Roger Bernadina had failed to back up Harper, a careless and crucial mistake. Rollins scored without even having to slide.

One night could chance the thrust of the rivalry between the Nationals and Phillies. The Nationals remain in first place, and the Phillies are playing out the string. They will face each other 11 more times. The team that once dominated the Nationals will have nothing to play for, except making them miserable in a new kind of way.