"I really didn't do anything different. I got good pitches to hit and hit them hard," Willingham said.
Dukes and Willingham didn't start the hitting frenzy, however. Chicago right-hander Carlos Zambrano started the game, and it turned out to be one of his worst outings, lasting 4 1/3 innings and giving up eight runs on seven hits.
Things started to go wrong for Zambrano in the second inning, when Wil Nieves hit a sacrifice fly to send home Willingham.
After Zambrano tied the score in the third inning when he homered off Nationals right-hander Garrett Mock, Washington poured it on in the fourth and fifth innings.
In the fourth, Willingham hit the ball out of Wrigley Field for his 20th home run of the season. Two batters later, Dukes drove in Belliard with a double.
"I love to get up there with guys on base," Dukes said. "RBIs mean a lot to me. It's not about the batting average and the home runs."
Dukes proved in the next inning how much he loves to drive in runs. He highlighted the six-run inning by hitting a grand slam off Aaron Heilman, making the score 9-1. Five of the six runs were charged to Zambrano.
"We have a good-hitting ballclub," interim manager Jim Riggleman said. "[When] facing a guy like Yovani Gallardo [on Monday], we passed up so many opportunities with him.
"Today we were given the same situation and we got Zambrano. We hit the ball well. A combination of that and getting [hits] off the end of the bat that fell in for us. It created big innings, bases-loaded situations and scoring situations that we passed up all day yesterday. Today we didn't pass them up."
But Chicago made the game interesting in the bottom of the sixth inning, as Mock gave up RBI hits to Kosuke Fukudome and Geovany Soto. Mock pitched 5 2/3 innings and gave up four runs on seven hits.
Riggleman still felt that Mock had an impressive outing because he cruised through the first five innings.
"Garrett was real good," Riggleman said. "He had a good breaking ball. He was aggressive with his fastball. He threw his changeup at the right time. He had another good performance. That's four in a row for him.
Washington added three more runs in the sixth inning off Sean Marshall as Willingham had an RBI single and Nieves drove in two runs with a single.
Willingham did it again in the top of the eighth inning by hitting a three-run homer off left-hander Tom Gorzelanny.
"That team swings the bat, they have some athleticism and they've been playing well," Cubs manager Lou Piniella said of the Nationals. "We've had a rough August. What can I say?"
It's true the Nationals have the worst record in baseball, but don't blame it on the offense. Entering Tuesday's action, Washington ranked sixth in the National League in offense. It could be even more fearsome if Dukes stays healthy and plays the game the right way.
"Elijah is a work in progress," Riggleman said. "Recognizing the breaking ball is key. He got one up in the zone and hit it well. When he can start laying off the ones low and away that are not strikes, he is going to be a force in the league."