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WASHINGTON -- Even Davey Johnson, at 70 the oldest manager in the majors, never heard of this one: The umpires got caught in a traffic jam.

That was the official reason given for the 16-minute delay at the start of what turned out to be his Washington Nationals' 5-2 victory over the Chicago White Sox on Wednesday night.

Johnson's shortstop, Ian Desmond, could empathize.

"I've been stuck in traffic many a time here in D.C. I'm surprised they got here as fast as they did," Desmond said with a smile. "It's always an adventure here."

Desmond had a triple and a pair of doubles, Bryce Harper homered, and Danny Espinosa provided his first two RBIs of the season, helping the Nationals improve to 5-0 at home. Jordan Zimmermann (2-0) limited Chicago to two runs and seven hits in seven innings. Both runs scored on groundouts.

"We threw a lot of fastballs inside," said Zimmermann, who is 7-0 with a 2.91 ERA in his last 13 home starts, "and got a lot of broken bats."

Johnson said the umpires "called in about 40 minutes before the game and said that they were a mile away, but it may take forever."

He added: "Didn't seem to bother Zim too much. Pitched a great ballgame."

Drew Storen pitched the eighth, and closer Rafael Soriano worked around a hit in the ninth for his fourth save in five chances.

Harper hit his fourth homer into the second deck leading off the fourth against Gavin Floyd (0-2), who allowed five runs and nine hits in 5 1/3 innings. Harper turned on Floyd's first pitch of the at-bat, an 86 mph offering that never stood a chance. With a "thwack!" off the bat, the ball arced into the second deck beyond right field, and Harper paused for a moment to watch his shot before sprinting around the bases.

"Early on, he's hacking. I think he's one of the highest-percentage (hitters) early on, so you kind of know that and you're making pitches," Floyd said, "and my cutter didn't cut like I wanted it to."

That gave the Nationals 11 homers in their last four games, 15 for the season. The 14 entering Wednesday were a franchise record through a season's first seven games.

Floyd struck out the next two batters, but then got into more trouble, giving up Desmond's double and Espinosa's single that gave Washington a 2-1 lead.

"It's a tough lineup," White Sox manager Robin Ventura said. "And when you get to that fifth or sixth inning, it's hard to get through it again."

Every Nationals starting position player reached base at least once; the only one without a hit, Kurt Suzuki, walked three times.

Harper's next time at the plate, in the fifth, he followed a single by Jayson Werth with a single up the middle of his own, this time on a 91 mph first pitch. TV replays showed Harper's bat split on impact with the ball, then broke completely as the wood slapped against his back on his follow-through.

Ryan Zimmerman followed with an RBI single to shallow right.

After Chicago drew within 3-2 on Alex Rios' RBI groundout in the top of the sixth, Washington chased Floyd in the bottom half by tacking on two more runs.

Desmond led off with a triple, Espinosa followed with an RBI double, Suzuki walked and Zimmermann sacrificed the runners over.

Floyd was done, and lefty reliever Donnie Veal came in to face Denard Span but gave up a run-scoring single.

"There were a lot of guys that had really good (at-bats)," Harper said, "and really came up big for us tonight."

Game notes

Rios' four-game homer streak ended. ... A smattering of applause from the crowd of 24,586 greeted the first announcement of Adam Dunn's presence in the White Sox lineup. He played in Washington in 2009 and 2010. Usually Chicago's DH, he sat out Tuesday's series opener and played left field Wednesday, going 0 for 4 with an RBI groundout in the sixth. ... Chicago 2B Gordon Beckham sat out after hurting his left wrist Tuesday. He's not sure how long he'll be sidelined. Jeff Keppinger started at second Wednesday, with Conor Gillaspie at third. ... White Sox pitching coach Don Cooper is still hospitalized with a stomach illness.