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WASHINGTON -- Chicago Cubs manager Lou Piniella has a remedy ready for the next time Alfonso Soriano's power stroke inexplicably disappears.

"We'll dislocate a finger a week if it gives us a three-run homer," Piniella wisecracked.

Soriano hit a go-ahead three-run shot in the sixth, connecting for the first time in almost six weeks, and the Cubs held on for a 6-5 victory over the Washington Nationals on Saturday night.

Soriano sent a first-pitch slider from rookie right-hander Jordan Zimmermann over the wall in right-center, erasing a 4-2 Washington lead. It was the 15th homer -- and first since June 7, a span of 121 at-bats, the second-longest dry spell of his career -- for Soriano. The outfielder missed Friday night's game with a swollen right pinkie finger after dislocating the digit diving back to first base the night before.

The blast came after Zimmermann fanned Milton Bradley on three pitches for the inning's first out. Catcher Wil Nieves said the ball didn't go where Zimmermann wanted, creating a fat pitch.

"It's a slider that didn't do anything," Nieves said. "We tried to throw down and away and it stayed in the middle. Soriano is a pretty good mistake hitter."

Piniella had two lineups penned when he arrived at Nationals Park on Saturday -- one with Soriano, one without -- and had to wait for Soriano to swing without pain in the cage. Considering the outcome, Soriano took his manager's good-natured threat in stride.

"I had to wait to dislocate one finger to hit a homer, so I don't know," he said. "But I feel very comfortable at home plate. I had bad first half, so I hope every bad moment I had will stay in the first half and I have a new second half with a better job."

Fill-in starter Randy Wells (5-4) worked five innings, allowing four runs on seven hits, walking one and striking out one. Wells started in place of Ted Lilly, who was scratched with a sore left knee.

Ryan Zimmerman had two RBIs for Washington, which fell to 0-3 under interim manager Jim Riggleman, who took over when Manny Acta was fired Monday. The Nationals, who couldn't protect a 4-0 lead, have lost four straight and nine of 10.

Mike Fontenot also homered and Ryan Theriot drove in two runs for the Cubs, who have won three in a row.

Carlos Marmol escaped a one-out, bases-loaded jam in the seventh and Kevin Gregg got Josh Willingham to ground sharply to third with the bases full to end the eighth. Gregg needed five outs for his 18th save in 21 chances.

Given the squandered lead and late opportunities, Riggleman couldn't fault the Nationals for not putting themselves in a position to win for the first time since July 11.

"We just haven't been able to get a run home," he said. "It's going to happen, though. I promise you it's going to happen."

The Nationals took a quick 2-0 lead off Wells in the first. Nyjer Morgan led off with a double, moved to third on Nick Johnson's single and scored Zimmerman's sacrifice fly. Johnson stole second and scored when Adam Dunn doubled to left-center.

RBI singles by Morgan and Johnson made it 4-0 in the second. Theriot's two-run triple cut the lead to 4-2 in the third.

In the Cubs sixth, Derrek Lee led off with a double, Aramis Ramirez reached on second baseman Willie Harris' error before Soriano's shot.

Zimmermann (3-5) lasted 5 1/3 innings, allowing five runs -- four earned -- on six hits. He walked one and matched a career high with eight strikeouts.

Fontenot homered off Jason Bergmann in the eighth. Zimmerman's sacrifice fly got Washington to 6-5 in the bottom of the inning.

Game notes

Instead of starting Monday against the Mets, Nationals LHP Scott Olsen will have his back tightness examined by Dr. James Andrews. Acting general manager Mike Rizzo said Washington would recall a pitcher from Triple-A Syracuse to make the start. ... Cubs RHP Ryan Dempster, on the 15-day disabled list since July 7 (fractured toe), threw a bullpen session Saturday and "felt OK," manager Lou Piniella said. ... Willingham was twice hit by pitches and has been plunked a team-high 10 times this year.