I agree that you can definitely tell that Rand is tired; he really didn't bring his 'A game' today. However, I also wouldn't overestimate the effect of this debate. More people may be tuning into the election as we go into the final week, but the proportion of undecided primary voters who will bother to tune into C-SPAN for a primetime Senate debate is quite small. Most viewers will be political junkies like us, who already decided who they were backing 3 months ago.
The most significant thing that can happen at this point is a candidate blowing up at someone or melting down under a question. Trey was trying hard to make Rand do that, and he thankfully failed. Rand did look a bit awkward at points, but really, Trey getting in snide remarks about knowing what 'Unite' is isn't going to be the game-changer he needs.
So, on balance, Rand may not have looked so hot, but Trey's the one who lost.