MELBOURNE — Dominic Thiem edged closer to his mum getting a kangaroo tattoo after the world No. 5 swatted aside an error-prone and underarm-serving Gael Monfils to book a maiden Australian Open quarter-final on Monday.

The two-time Roland Garros finalist proved too wily for his experienced French opponent, crushing him 6-2, 6-4, 6-4 on Rod Laver Arena.

Thiem revealed that he made a pact with his mother Karin last year that each time he won a title she would get a tattoo to mark the occasion.

"After a pretty bad start to the season last year after some losses she said after a long trip to Indian Wells from Rio, all really jet-lagged, that if I won that she would get a tattoo," the Austrian said.

"I ended up winning that one so this tradition started."

She has since got tattoos of an eagle feather to mark winning in the United States and a panda after he claimed a title in China.

Asked what she would be marked with if he clinches the Australian Open, he replied: "For sure a kangaroo."

Thiem has long had the measure of Monfils, winning all five of their previous encounters, and the 10th seed had no answers on a hot Melbourne day, making 32 unforced errors.

"I played my best match so far, I had a good feeling," said Thiem, the first player from Austria to reach the last eight at Melbourne Park since Stefan Koubek in 2002.

"But the score looks much easier than the match was. I always play my best tennis against Gael."

Monfils is a nine-time Grand Slam quarter-inalist but only one of them came in Melbourne and he never looked like reaching a second.

The Austrian, targeting a maiden Grand Slam crown, went a break up for 2-1 in the opening set and then grabbed another as Monfils struggled to deal with Thiem's accurate and varied first serve.

With Thiem pressing hard again in the second set, Monfils tried an underarm serve at 40-30 in game three. It worked, catching the Austrian off-guard.

But it only delayed the inevitable. With Monfils appearing to struggle in the heat, Thiem created four break points in game seven and the Frenchman finally succumbed by missing an easy net volley.

The third set followed a similar pattern with Thiem breaking early and quickly completing a routine victory.

Thiem dumps Muster

after barely two weeks

Dominic Thiem has dumped 1995 French Open champion and former world No. 1 Thomas Muster as an adviser just weeks after hiring him, but insisted Monday "nothing bad happened".

The world No. 5, who is chasing a maiden Grand Slam breakthrough at the Australian Open, brought Muster on board this month after he served as captain of the Austrian team at the inaugural ATP Cup.

He was due to make himself available for 20 weeks this year, working alongside Thiem's coach Nicolas Massu.

"Well, nothing bad happened there. But we already said before we started the relationship that if it doesn't work out, we're gonna stop it, and that was the case," Thiem said after moving into the Australian Open quarterfinals.

"I mean, I think it's always difficult, especially for me at the stage where I am, to find something perfect to add to my team.

"And I just had the feeling that it's not going to work out together, and that's why we finished. So that's all."

Muster cryptically told Eurosport in an interview: "It is like this: There are houses which look nice from the outside, wonderful from the outside, but you rarely know who lives inside.

"He (Thiem) has improved a lot, but he has to catch up in the technical, physical and foremost in the mental area," he added.

"To be honest I have seen myself in this role for the next two years. Why he has chosen differently — I know why, but I don't want to say the details." — AFP