Why Milos Raonic was heartbroken...

A gallant Milos Raonic was left heartbroken by his Australian Open semi-final loss to Andy Murray on Friday, having pushed the Scot to his limits before a leg injury took the game out of his hands.

The 13th seed played majestically for much of the four-hour classic at Rod Laver Arena but strained an adductor muscle midway through the third set and eventually folded 4-6, 7-5, 6-7(4), 6-4, 6-2.

He had a medical time-out early in the fourth set and was worked on by a trainer at changes of ends.

The frustration ultimately told when he smashed his racquet in dismay after being broken early in the fifth set.

"It's unfortunate, probably the most heartbroken I felt on court but that's what it is," the downcast 25-year-old told reporters, his eyes red and voice cracking.

"I think maybe that's why I sort of lashed out the way I did after the start of the fifth set.

"I guess that was the whole frustration of everything getting out."

Having had the World No 2 on the ropes for much of the match would have only added to Raonic's disappointment.

The first Canadian man to reach the semi-finals at Melbourne Park, the Carlos Moya-coached Raonic underlined his claim as one of the top young talents in the game by mowing through a tough draw and upsetting 2014 champion Stanislas Wawrinka in the fourth round.

It was of little consolation for the 25-year-old, however, who was left on the sidelines for much of last season due to a string of injuries.

"I'm in a much better state (than) where I was 18 months ago when I was in my first semi-final of a grand slam," said Raonic, the 2014 Wimbledon semi-finalist.

"If this didn't happen 20 minutes ago, there's a lot more positive to take from the situation than there is negative by magnitudes.

"With the way I've sort of started off this year after the difficulties I had, whatever it was, three months ago, not finishing the year, many other aspects, not knowing where I stood, this was the most ideal way to start.

"You can't take away that sort of hurt from the way the story played out today."