Emotional Tiafoe eyes Nadal scalp

An emotional Frances Tiafoe said on Sunday he had already changed his parents' lives and now he was motivated to do the "same for me" ahead of a quarterfinal with Rafael Nadal at the Australian Open.

The American celebrated his 21st birthday by beating 20th seed Grigor Dimitrov in four sets and then broke down as he revealed how he had supported his mother and father, who are both immigrants from Sierra Leone.

"It means the world," said a tearful Tiafoe, voice cracking, after stunning the Bulgarian 7-5, 7-6 (8/6), 6-7 (1/7), 7-5 in 3hr 39min.

"I worked my a** off, man. I told my parents 10 years ago I was gonna be a pro tennis player and change their life."

World number 39 Tiafoe described his unusual path to the last eight of a Grand Slam for the first time in his fledgling career.

"Obviously I wasn't a normal tennis story," he told reporters. "The beginning of my career, I was playing for them, trying to do everything for my family."

He described how at the age of 19 he managed to turn around things for his struggling parents.

"In March 2017 I bought a house in Maryland for my mom. My dad is in an apartment in Orlando," he said of his janitor father.

"So, yeah, that was big. Getting us out of... you know, just put us in better situations. I was able to do stuff like that.

"Obviously I put them in a great place. Now I'm trying to do it for me."

The aggressive American upset the 20th seed in four high-quality sets that saw multiple breaks of serves and an avalanche of breathtaking winners.

"I would have been mad if I had lost on my birthday," he added.

After celebrating his win by ripping his shirt off, beating his chest and showing off his muscles, LeBron James-style, Tiafoe then seemed a bit embarrassed.

"I said I wasn't going to do that again," grimaced the young giant-killer, who knocked out fifth seed Kevin Anderson in the first round.

Tiafoe admitted that winning on his birthday meant he would have put celebrations on hold to prepare for the daunting prospect of facing the 17-time Spanish Grand Slam champion.

"I can't do anything tonight. He's going to run me like crazy," he said. "I'd better go to bed now."