I thought for a moment that it might be the best win in ranking terms of anyone including Muzza, but he did beat Ferrer ( WR 7 ) and Melzer ( WR 11 ) at the Australian Open. Best win of anyone since.
Stunning win - best I can recall in ranking terms by a Brit outside the top 100 for over a decade. Ian Flanagan beat Mark Philipoussis here in 2004, but he was ranked slightly lower than Wawrinka. Mark Petchey beat world no.2 Michael Stich in 1994, and there may well be one or two others over top 15 players since, but I cannot think of them off the top of my head.