It's been a long season for first-year Chicago Cubs manager Dale Sveum, and it's not over yet.

Sveum's team yielded six Washington homers for the second consecutive game and dropped a 9-1 decision to the NL East leaders on Wednesday night for its fifth straight loss.

Sveum was highly complimentary of the Nationals, who own the best record in the majors at 84-52.

"This is by far the best team we've played all year," he said. "It's like an American League lineup, too. Guys that hit the ball a long way and grind at-bats out and take advantage of any mistake that is thrown.

"That's pitching, bullpen, starting pitching, defense, speed, power, that's as good a team as there is in the National League.

Sveum wasn't around for the end of the game. He was ejected in the fifth by plate umpire Larry Vanover for arguing balls and strikes.

"I just didn't appreciate him eyeballing our dugout for absolutely no reason at all," Sveum said.

"I just don't think that's right when you're looking in our dugout for no apparent reason at all. Nothing at all to warrant that at all."

Gio Gonzalez pitched seven scoreless innings for his 18th win and Bryce Harper hit two homers for Washington, which has won four straight and maintained a 7½-game lead over Atlanta in the division. Adam LaRoche kept up his tear at the plate with three hits, including his fifth homer in the past five days.

The 19-year-old Harper had his second multihomer game. Previously, only Mel Ott and Ken Griffey Jr. had accomplished that feat as teenagers.

Gonzalez (18-7), who shut out St. Louis on five hits in his last start, allowed only three singles and struck out nine without a walk while matching Mets knuckleballer R.A. Dickey for most wins in the majors. Dickey beat the Cardinals 6-2 earlier in the day.

Craig Stammen worked the final two innings and allowed a ninth-inning homer to Anthony Rizzo, his 11th.

Gonzalez did not give up a hit until Darwin Barney led off the sixth with a single past third baseman Ryan Zimmerman.

Starlin Castro singled off second baseman Danny Espinosa's glove with two outs in the seventh and Welington Castro followed with a single to left. Gonzalez finished the inning by striking out Josh Vitters.

The Nationals scored in the first on LaRoche's RBI single.

Washington equaled a club mark by hitting three home runs in the third off Chris Volstad (2-10). Roger Bernadina led off with his fourth of the season. Harper followed with his 16th. Zimmerman singled and LaRoche hit his 28th homer.

Harper hit his 17th with one out in the sixth against Michael Bowden.

Ian Desmond and Espinosa hit back-to-back home runs to start the seventh off Blake Parker.

Volstad allowed five runs and nine hits in five innings. He had won his previous two starts.

"That's a tough lineup and he couldn't keep the ball down today, that's the bottom line," Sveum said.

Volstad was wary of facing the Nationals, who scored eight or more runs in three of four games against St. Louis.

"They put up runs all over the place against them, too," Volstad said. "They're a hot team. A good team and they're hot. It's a tough combo, but you've still got to go out there and make good pitches."

NOTES: Harper's 17 home runs are the third-most by a teenager. Only Tony Conigliaro with 24 and Ott with 18 hit more. ... Vitters is in an 0-for-25 skid. ... Chicago is 17-51 on the road. ... Nationals RHP Jordan Zimmermann (9-8, 3.01 ERA) will face Chicago RHP Justin Germano (2-5, 6.30 ERA) on Thursday.