That brought up Jones, who laced a 1-1 pitch into right field for an RBI, and Pittsburgh went on to salvage one victory in their three-game series.
Walker and Michael McKenry each socked a solo homers for the second-place Bucs, who came into the contest trailing National League Central-leading Cincinnati by 2 1/2 games.
Dempster, the subject of trade-deadline rumors, lost his second straight start, yielding three runs on five hits in a six-inning effort.
Anthony Rizzo bashed a two-run homer to supply the Cubs' offense.
Celebrity Breakups and divorces of 2014 [PHOTOS]