Maturing Andy Murray moves quietly into last eight

For someone who has admitted to having problems controlling his emotions, Andy Murray has shown a growing maturity throughout the Australian Open.

There has been the occasional self chastising. But on the whole he has quietly gone about his business through the tournament, except for one particular moment in Sunday's fourth round 7-6 6-3 6-2 victory over giant American John Isner.

Already leading by two sets to none, he let out a sustained yawp, and jigged away on his heels, when he sealed the first break in the deciding third set with a reflex backhand winner.

"You just kind of react. It's just instinct. You just chase the ball down (and I got) good contact on it and it obviously went for the winner," a smiling Murray told reporters when asked about the reaction.

"I'd had chances the first two service games to break him and didn't quite take them. So, yeah, happy with that."

Murray, who is yet to drop a set and has advanced to the quarter-finals for the first time, said he felt it was a sign of growing maturity.

"I have concentrated well in all of my matches. ... Not a whole lot in my game's changed.

"Sometimes in the past, when I was sort of 18, 19, you know, might have been getting worked up or not thinking about what I should be doing on the next point and worrying about what happened in the past."

Now, it's just focus on each point. So you make the right decision more often.

"I guess it's a maturity thing. You learn to deal with the tight situations better and your focus holds for longer."

On Sunday, the 22-year-old Scot had few problems with the 2.06m (6ft-9in) tall Isner, nullifying the effects of 14 aces by cleverly working him around the court and mixing delicate touch with laser-like accuracy.

On several occasions Isner, who won the Auckland Open before coming to Melbourne Park, was left wrong footed by Murray's tactics.

"He mixes it up (and) ... wasn't hitting a real big ball out there. Kind of just dinking and dunking it around the court," Isner said.

"And I felt like I wasn't able to get a good rip at the ball a lot of the time because of what he was doing with it.

"He played pretty well (and) got to a lot of balls. That game he broke me in the third set was insane, the shots he hit there.

"He's a good frontrunner, as well. To get down two sets to love is tough against him."