With a series sweep, the Pirates would three games above .500 heading into the All-Star break; if they themselves were swept, they would be back at .500.
The series, along with the next one against the Houston Astros, represents a big opportunity. The Cubs are 36-53, and their pitching has struggled mightily; in this series, the Pirates will face journeymen Rodrigo Lopez and Ramon Ortiz, sandwiched around Ryan Dempster on Saturday. That's not exactly a fearsome bunch. (When I was looking at the probables, I actually saw "Ortiz" and thought, "That can't be Ramon Ortiz, can it?" But it was indeed.)
The Pirates are currently one game behind both St. Louis and Milwaukee and could claim a share of first place if they win Friday and both the Cardinals and Brewers lose.