Top performances right throughout the team, but I'll plump for O'Brien. Excellent performance, was constantly tormenting the Killie defence, and of course got the two goals.
If Humphrey had been on earlier, or had started and played like that throughout, then he'd have been in with a shout as well. The Killie left back must have been praying for the final whistle as the Humph tore him again and again.
If both those two can maintain that level of performance then, with Humphrey on the right and O'Brien on the left, we could seriously start ripping the c**t out of full-backs throughout the SPL on a weekly basis. And with two big forwards in the box, a decent number of goals would inevitably follow.