CHICAGO -- The Pittsburgh Pirates have struggled almost everywhere this season -- except Wrigley Field.
Walker went 4-for-5 with four RBIs and three runs scored for the Pirates, who won for only the fifth time in 43 road games and ended a 14-game losing streak away from PNC Park.
"It's been hard for us to win on the road recently, but when we can do something like this it's good going forward for confidence," Walker said. "The biggest thing in a series is trying to win that series and now we have an opportunity to do that tomorrow."
Koyie Hill hit a two-run homer for the Cubs, who have lost 13 of 16 at home.
The Cubs are one of the few teams the Pirates have had success against lately. Pittsburgh is 10-4 against Chicago this season and has won 12 of 16 at Wrigley Field dating to a doubleheader sweep on Sept. 30 last year.
The only teams the Pirates have a winning road record against this season are the Cubs (5-3) and Colorado Rockies (2-1). Pittsburgh is 7-48 against the rest of its opponents away from home.
"They have our number for sure," Cubs starter Ryan Dempster said. "The easiest thing for us is to put tonight behind us as fast we can and come out tomorrow and win a game and win a series. We can't worry about games we played the beginning of the year or a month ago, let alone a day ago."
Pirates starter Jeff Karstens (3-10) avoided matching the longest losing streak in the majors this season. He pitched six strong innings and allowed two runs on four hits after missing his previous turn with a fatigued arm.
The right-hander came into the game 0-8 with a 5.40 ERA in his last 10 starts -- a stretch that began with a loss at Wrigley on June 29. Atlanta's Kenshin Kawakami and Baltimore's Brian Matusz are the only pitchers to drop nine consecutive decisions this season.
"I feel better, I don't know if I feel fresher. I didn't really have my legs underneath me until the second inning," Karstens said. "I don't know. Missing that start made my arm feel a lot better. Now it's just a matter of grinding it out and getting through the season."
Jose Tabata was 3-for-5 with three runs and two RBIs for the Pirates, who lost 14-2 to the Cubs on Monday night.
"I think it would be easy to let yourself slip mentally and physically into the place where when things go bad you fall into a hole, but I think this group here and guys who have been around this game for a long time know we're going to fight to grind it out. It's part of our nature," Walker said.
With a 14-2 lead in the eighth, Pirates reliever Sean Gallagher allowed five runs. He gave up a pinch-hit RBI double to Micah Hoffpauir and a pair of RBI singles to Starlin Castro and Xavier Nady before being lifted.
Dempster (12-9) had his worst outing of the season. He allowed a season-high seven earned runs and seven hits in three innings, his shortest start this year. Dempster had won his previous four decisions.
The Cubs (56-77) fell to 21 games under .500.
"The job is still the same coming to work. You've got to do your job the best you can. It doesn't say in your contract I'll try as hard as I can as long as we're in it," Dempster said. "Obviously, we would like to be in a better position, but there are still plenty of ballgames left and we have a month left in the season, go out there and play hard every day and try to win as many ballgames as we can."
The Pirates scored four times off Dempster in the first inning. Tabata walked and advanced to third on Walker's single. Jones hit a broken-bat comebacker to Dempster. Tabata scored as Dempster bobbled the ball and had to settle for getting Jones at first for the second out of the inning.
In the third inning, McCutchen hit a two-run single to give the Pirates a 7-0 lead.
Cubs reliever Marcos Mateo didn't fare well, either. He gave up a single to Walker, then Jones homered to left for his 20th of the season.
Walker tagged Mateo with a two-run shot to give the Pirates an 11-2 lead in the sixth. Tabata added another RBI single and Walker had a two-run double off reliever James Russell in the seventh.
Cubs right-hander Carlos Zambrano pinch-hit for Dempster in the third and grounded out. ... Walker hit his eighth homer of the season.