15-0 - 40-0 were all unforced errors from Monfils, Andy's game is apparently frustrating him at the moment. Andy is giving him no pace so Monfils is having to generate all the power on his shots on his own and is making errors.
Gael is playing very flat; he looks tired. Murray is having such an easy time because Gael just doesn't seem to have the energy to compete like he did in Rome.
If he was Murray might not have won the first set considering how many free points he's gotten on Gael's errors.
He isn't doing anything special, but Gael is feeding him points on errors.
Credit to Gael becuase his game has improved quite a bit, he's coming to net, playing much like he did in Rome but he's too flat to give anything.