John McEnroe believes Andy Murray is one of just three players who can win the US Open - but admits Roger Federer still holds the upper hand.
Murray was finally due to begin his bid for a first Grand Slam title against Slovakia's Lukas Lacko today, with Federer having already cruised into the second round on Monday evening.
World number one Rafael Nadal is the other player McEnroe thinks can lift the title on September 12, but he and Murray will have to do it the hard way after being placed in the same half of the draw, the other half to Federer.
"Federer is not going to have to deal with both of them, which is good for him," McEnroe said. "How much will Rafa and Andy beat up on each other in the semis?
"I would be very surprised if one of those guys did not win it. Andy can absolutely win it - if it doesn't happen this year, maybe next year."
Murray recently sacked coach Miles Maclagan and went on to defeat Nadal and Federer in consecutive matches to defend his Masters series title in Toronto.
And McEnroe added on BBC Radio Five Live: "The difference with Andy is his willingness to go after the ball, to be more aggressive.
"This is something he may have been thinking about for a while.
"I think it was time maybe. Maclagan did a good job, like (Mark) Petchey before him and now it's time for the next step. It seems like a good thing to try."
Murray and Lacko have never played each other on tour before, but world number 71 Lacko has recorded some impressive wins this year, including victories over Marcos Baghdatis in the first round of Wimbledon and former world number one Lleyton Hewitt in Atlanta.
However, he lost 6-2 6-2 6-2 to Nadal in the second round of the Australian Open in January - where Murray lost in the final to Federer - and the British number one will be hoping for a similarly one-sided victory to get out of the scorching early-afternoon sun as soon as possible.