Vasek looked better than Isner in the rallies (when there were any). But Vasek got only 50% 1st serves in, and seemed to have some kind of lapse after he failed to break in the first Isner service game of the 3rd set.
He started to come out of it but only after he was broken. These kids are so up and down in their confidence.
As for the 50%, his % was only low in set 1, so that's why it looks worse overall than it really was.
Not quite, Isner really stepped up his game after that and his 1st serve was on major fire.