They really don't want Pearson to come in with runners on. He is also very prone to walks so not ideal roll for him. He could have came in instead of Bass for that situation.
Apparently we all missed the balk. I know Vladdy took second. The broadcast played it off as defensive indifference. It was not called out at the time.
Pushing Bassit makes a lot more sense then using the pen for 4 innings. No day off coming until May 8th. 4 game series at Fenway needs a lot of fresh arms.