MELBOURNE, Australia -- Quarterfinal action begins Tuesday at Melbourne Park with Frances Tiafoe looking to become the first American man to reach the Australian Open semifinals since Andy Roddick in 2009.
Tiafoe faces 17-time Grand Slam champion Rafael Nadal in prime time at Rod Laver Arena (5 a.m. ET on ESPN2).
Local sensation Ash Barty, who meets eighth seed Petra Kvitova, is also in action, while Stefanos Tsitsipas -- the conqueror of Roger Federer -- returns to center court to play Spaniard Roberto Bautista Agut.
How to watch
Day session
ESPN3 & ESPN+: Starting at 7 p.m. ET
ESPN2: Starting at 9 p.m. ET
Night session
ESPN2: Starting at 3 a.m. ET
Full Day 9 schedule
Key storylines
Tiafoe faces mammoth challenge in world No. 2 Nadal
Before the tournament began, Tiafoe had won just five Grand Slam matches in his career. Eight days later, he's already up to nine ... and counting.
The 21-year-old American has quickly become a fan favorite at Melbourne Park and has a chance of progressing to an unlikely semifinal -- if he can beat 2009 Australian Open champion Nadal on Tuesday night.
Tiafoe's come-from-behind win in the second round over fifth seed Kevin Anderson has sparked an inspired run Down Under. He backed it up with further upsets over Italian journeyman Andreas Seppi and world No. 20 Grigor Dimitrov.
Nadal has been just about the most impressive player to date, having earned comfortable straight-sets wins in all four of his matches. But the fact that Tiafoe has nothing to lose could pay enormous dividends.
Local hope Barty looks to continue dream run
It's been 10 years since an Australian last ran this deep at the Australian Open.
Barty, 22, delighted Australians after knocking off Maria Sharapova on Sunday and advancing to the quarterfinals of her home Grand Slam.
The Queenslander will meet two-time Wimbledon champion Kvitova in the final eight, an opponent she knows all too well. The pair played earlier this month in the Sydney International final, a tight match that went the way of Kvitova, 1-6, 7-5, 7-6 (3).
Kvitova has yet to drop a set in Melbourne, while Barty's only blemish came in the first set against Sharapova.
Given that Barty has never reached a Grand Slam semifinal and Kvitova hasn't been to one since 2014, there's no shortage of motivation for either player.
Can Tsitsipas back up his heroic effort?
Tsitsipas is responsible for the most surprising result of the tournament after he took out 20-time Grand Slam champion Federer on Sunday.
Playing fearless tennis, Tsitsipas was aided by some sloppy play from Federer to take the match in four sets and become the first Greek player to reach the quarterfinals of a major. But he can't relax just yet.
Tsitsipas hopes a letdown is not in store when he faces 22nd seed Bautista Agut on Tuesday afternoon.
The Spaniard, who took out 2018 runner-up Marin Cilic in the fourth round, has had to play three five-set matches en route to this stage.