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WASHINGTON -- Looking for a strong start in the second half, a weekend trip to lowly Washington was exactly what the Chicago Cubs needed.

Alfonso Soriano's two-run homer keyed a seven-run fourth inning and Chicago completed a four-game sweep of the Nationals with an 11-3 victory Sunday.

Soriano's 16th home run, his second in two games after a drought of 120 at-bats, began the biggest inning of the season for the Cubs. Starting pitcher Kevin Hart also contributed by faking a bunt and punching an RBI single.

"When you get ahead of them, that's where you want to be because it seems like it kind of takes the wind out of their sails," Chicago's Jake Fox said. "That home run put us ahead of them and we stayed ahead of them all day."

Fox had a fine day, too, with three hits and a career-high four RBIs. His three-run homer in the sixth gave Chicago an 11-2 lead.

Adam Dunn hit his 24th homer but Washington dropped to 0-4 under interim manager Jim Riggleman, who took over when Manny Acta was fired at the All-Star break. The Nationals have the worst record in the majors at 26-65. They've lost five straight and nine of 10.

A year ago, Riggleman took over for the fired John McLaren in Seattle and won three of his first four games. The first four with the Nationals have been more difficult.

"Today was a step backward," Riggleman said. "It was a breakdown all the way around."

Mike Fontenot and Micah Hoffpauir also had three hits for the Cubs, who outscored Washington 26-11 in the sweep. Chicago has won six of seven.

After the game, the Cubs boarded a bus to Philadelphia, where they'll play baseball's hottest team. The Phillies have won eight straight.

"We'll go into Philly with some momentum, playing better on the road," Cubs manager Lou Piniella said. "They're hot as heck, so we'll see."

Chicago had 16 hits, equaling a season high.

"It's a good team over there," Washington third baseman Ryan Zimmerman said. "They're a better team."

Hart (1-1), who spent the All-Star break pitching at Class-A Peoria, was recalled to make the start. He pitched five innings, allowing two runs and five hits while walking five and striking out one. The hit and RBI were the first of Hart's career.

It was the walks -- not his hit -- that Hart wanted to talk about.

"They're killing me," Hart said. "I've been fortunate the last few times out to pitch out of some jams. I know if I keep it up I'm not going to be as fortunate every time."

Chicago's seven-run fourth also included two Nationals errors and RBI singles by Kosuke Fukudome, Derrek Lee and Fox and a sacrifice fly by Ryan Theriot.

Garrett Mock (0-3), who was summoned from Triple-A Syracuse after winning five straight there, allowed seven runs -- four earned -- in 3 1/3 innings for Washington.

The Nationals scored in the second and third on sacrifice flies by Alberto Gonzalez and Zimmerman. Dunn connected in the seventh.

Game notes

Washington designated RHP Julian Tavarez for assignment and called up RHP Logan Kensing from Syracuse on Monday. ... J.D. Martin will make his major league debut Monday as the Nationals' starter against the New York Mets. Martin was 8-3 with a 2.66 ERA at Syracuse. To make room for him, Washington put LHP Scott Olsen on the 15-day disabled list with a back injury. ... To make room for Hart, the Cubs sent OF Sam Fuld to Triple-A Iowa. ... SS Cristian Guzman, who missed the previous two games with bunions, pinch hit in the fourth inning. ... The Nationals have left the bases loaded four times in the past three games. ... Dunn's 24 homers are the most by a Nationals left-handed hitter in a season. ... Piniella sat slumping OF Milton Bradley. "I had a nice talk with him today, and tomorrow we'll start working on some things that I think will help him," Piniella said.