When a Six-Run Inning Isn't the Pitcher's Fault

In Saturday's game versus the Rays, Jon Lester got off to a pretty good start. After giving up a two-run homer to Evan Longoria in the 1st, Lester regained his form and threw three scoreless innings. Until the 5th inning, that is, when everything fell apart. When the bleeding stopped, the Rays had scored six runs and had taken an 8-1 lead. The funny thing is, those six runs weren't really Lester's fault.
How can a pitcher give up six runs and not take most or all of the blame? You have to fault the defense, right? Nope, not their fault either. The Sox didn't commit an error in the inning, and they only made one little mistake that could be called a defensive "miscue". If not the defense, then, who was responsible for those six runs?
Luck.