Murray should win this one comfortably, but that brings with it pressure of its own, against Harrison Murray was playing a future top player, there was always the chance the match could go more than 3 sets. However after seeing the ease with which the top 3 have eased through, the pressure is on Murray to put in a similar perfomance against Vasselin.
Vasselin has shown he doesnt mind pressure he took out Juan Martin Del Potro just after he won the Open in 2009. I expect Murray to come through but keeping energy in reserve will be huge for him if he gets extended here then its going to get harder and harder to repeat the last two years, the pressure is on him big time, how he responds we are going to see very soon.
The difference is that the top 3 all had easy rides in R1, although Federer was sailing a little close to the wind in his first set before he finally got the better of his opponent.
I really don't see why Andy should feel pressurised in this match. In fact playing someone as good as Harrison was probably to his benefit, even although it was unfortunate that he had to go four sets in stiflingly hot and humid conditions. Luckily the temperature will be lower tomorrow, and Andy willl be looking to get the match over with as quickly as possible. He's extremely fit so hopefully will have recovered from the Harrison match.
As for Vasselin beating del Potro, I wouldn't read anything into that. I think his exertions in the USO final took a great deal out of him both mentally and phyisically.