WASHINGTON — John Lannan will probably want to forget his first start as a visitor at Nationals Park.

The left-hander had one of his worst outings of the season against his former club Friday night, allowing eight runs in the Philadelphia Phillies’ 9-2 loss to the Washington Nationals.

“This wasn’t a great day,” said Lannan, who lasted five innings. “Falling behind from the beginning. There was times when I thought I found something I could kind of build off of, but then I kind of lost it.”

Lannan (3-5), who spent his first six major league seasons with the Nationals, allowed multiple home runs for the first time in 13 starts this season.

Anthony Rendon hit a two-run shot and Ryan Zimmerman added a solo homer, both in the second inning, before the Nationals scored another run off Lannan in the third and chased him after scoring four more in the fifth to make it 8-1.

Dan Haren (7-11) allowed two runs and four hits over seven innings for his first career win against the Phillies in eight starts. He struck out seven without issuing a walk to send Philadelphia to its seventh loss in nine games.

“I wouldn’t say his stuff was any different,” said Phillies manager Charlie Manuel. “His command was definitely better and his pitch selection was better. He threw us a lot of soft stuff. When he got ahead of us, he threw us a lot of sliders and splits and stuff. He did a good job with it really.”

Chase Utley singled in Philadelphia’s first run in the fourth inning, and Cody Asche’s seventh-inning grounder cut it to 8-2.

Reliever Raul Valdes allowed Washington’s final run in the eighth as the Nationals snapped a four-game losing streak.

Lannan, who had a win in two previous starts against the Nationals in Philadelphia, allowed season highs in runs, walks (five), and home runs in the return to his former home park.

While a National, he spent most of 2012 with triple-A Syracuse, before signing as a free agent with Philadelphia last December.

He had allowed one run or fewer in three of his last four starts before the All-Star break, but has struggled in the second half. He said his performance wasn’t affected by any added pressure of returning to Washington.

“Being back in D.C., it’s a great city,” he said. “I had a good time here, but you know, it really didn’t affect the way I felt out there.”

The Nationals, meanwhile, signed Haren to a lucrative one-year deal this offseason instead of bringing Lannan back as their fifth starter.

Haren is 3-0 with a 1.29 ERA in his last three starts after struggling for the first part of the season. His ERA dropped to 4.99, below 5.00 for the first time since mid-May.

Before Friday’s matchup, Haren sported a 0-4 record with a 5.54 ERA in seven career starts against Philadelphia. That included three starts this season, all ending in Washington losses.

This time he held the Phillies without a hit until Michael Young’s one-out double in the fourth. Utley followed with an RBI single, cutting the lead to 4-1.

Rendon hit a two-run homer off Lannan in the second inning after the umpires confirmed it on instant replay. Three batters later, Zimmerman hit his 13th of the season, which landed several rows deep in the left-center stands.

Adam LaRoche snapped a 0-for-16 lifetime skid against Lannan with an RBI double in the third. Denard Span’s two-run single capped a four-run fifth inning. Bryce Harper added an RBI single.

The Nationals went 6 for 10 with runners in scoring position, and also benefited from Lannan’s bases-loaded walk of Haren to score a run and bring Span to the plate in the fifth.

Ryan Mattheus and Ian Kroll each pitched one hitless inning of relief for Washington.

Notes: Manuel remains one win short of 1,000 victories for his career. ... LHP Cliff Lee (10-5, 3.13 ERA) opposes Nationals RHP Taylor Jordan (1-3, 3.76 ERA) on Saturday.

I've worked at newspapers since 1985. Mostly in N.J., but with an eight-year pit stop in N.C. I've been at The Press since 1997.