"It helped us win a baseball game today, and let's hope it becomes contagious here in the last month or so of the season," manager Lou Piniella said.
"We need to put together a semblance of a good winning streak and go from there. Right now, a win feels really good, believe it or not."
Bradley gave the Cubs a 2-1 lead in the third with a two-run homer off Livan Hernandez, but the Nationals tied the score in the sixth when Cristian Guzman touched Rich Harden for an RBI single.
Chicago put runners on first and third with one out in the seventh for Bradley, who hit a soft ground ball to third off Jason Bergmann (2-3). Ryan Zimmerman charged and fielded the ball cleanly, but his throw home sailed wide, allowing Hill to score the go-ahead run.
With the often-erratic Carlos Marmol preparing to enter the game in the ninth inning, the Cubs needed some insurance runs and got plenty of them. Kosuke Fukudome singled, and one out later, Jeff Baker hit a grounder to first. Pitcher Jorge Sosa didn't get over to cover first on time, and Baker picked up an infield single.
"We have done a heck of a job taking care of the details of the game and, today, we didn't," Nationals manager Jim Riggleman said. "You see what happens."
Hill came up next and drove in two with a double, and the Cubs plated four more in the inning to go ahead, 9-2.
"I think at this point, any time you get three hits in an inning, it's something to build on," Hill said. "It was nice to have that big inning, definitely, late in the game, in a close ballgame, to give our guys a little breathing room."
Marmol, who recently was appointed as the team's closer, walked the first three hitters he faced in the ninth and surrendered two runs.
John Grabow had kept Washington off the board in the eighth and Angel Guzman (3-3) earned the win with a scoreless seventh in relief of Harden, who held the Nationals to two runs in six innings. Harden has allowed two earned runs or fewer in eight straight outings.
He got off to a rough start, loading the bases with no outs in the first, but he struck out Adam Dunn and escaped after allowing one run on Josh Willingham's sacrifice fly.
"I've been feeling pretty good," Harden said. "I just go out there and throw strikes. The big thing for me is getting through that first inning without any problems. That's when I've been throwing most of my pitches for a few games here."
Bradley continued to produce at Wrigley Field, where he has hit about 100 points better than on the road and smacked eight of his 11 home runs. He was 2-for-23 on the Cubs' last road trip but went 4-for-4 on Tuesday and 1-for-4 with a walk Wednesday.
Hill has been splitting time with Geovany Soto at catcher since Soto returned from the disabled list Aug. 7. Although he is known more for his glove, Hill reached base all four times he came up and scored two runs.
"It always feels good to contribute, but it feels even better to win," Hill said. "That being the pressing issue around here -- I think it always is -- but it's nice to get back on the right track."
Just like everyone else in the Cubs' clubhouse, Hill is not giving up on the season yet.
"We want to put together a winning streak," he said. "We want to win ballgames. Just because you're running out of time, it doesn't mean there's any more emphasis on it, it just means you're running out of time and you don't have a whole season to get on that roll. You have to get on that roll now."