The Marlins have won eight of their last 10 games to surge into NL wild-card contention and were buoyed by the addition of Washington first baseman Nick Johnson minutes before Friday's trade deadline. He's expected to be in the lineup Saturday.
The score was 2-all when Carlos Marmol (2-2) came into the game in the eighth with a scoreless streak of 8 1-3 innings, but he walked the first two batters. Dan Uggla scored from second on Baker's hit, and Helms doubled to hike his average as a pinch-hitter to .387.
Florida won despite striking out 13 times, stranding nine runners and committing an error for the first time in nine games.
Brendan Donnelly (1-0) retired two batters in the eighth for his first NL victory, and Leo Nunez pitched a hitless ninth for his ninth save in 12 chances.
Volstad retired the first 12 batters and took a shutout into the seventh, but Jake Fox's two-out, two-run homer tied the score at 2-all.
The hit brought a roar from the crowd of 25,024, with many of the fans clad in Cubs blue. It was the 22nd homer allowed by Volstad, who went 6 2-3 innings.
Florida took a 1-0 lead in the second. Jeremy Hermida led off with a single and scored on Volstad's two-out double
- the pitcher's first career RBI and extra-base hit. Jorge Cantu hit a two-out homer in the third, his 11th.
Cubs starter Rich Harden tied a career high with 11 strikeouts but departed for a pinch hitter after five innings trailing 2-0.
