Dating to the latter portion of last season, Lester and Ross have worked well together. In his first two starts this season with Pierzynski, Lester had a 3.86 ERA and a .347 opponents' batting average. With Ross, he has a 2.39 ERA and a .194 average.
Why the switch?
Pierzynski is 9-for-22 lifetime (.409) against Mark Buehrle, his longtime batterymate with the White Sox.
"He's had quite a bit of success against Buehrle and in a stretch where we're trying to generate as much offense as possible," Farrell said. "That's where we are in the lineup today."
Of late, Ross has struggled mightily at the plate, providing just three hits in his last 27 at-bats.