In addition to this battle between two of the world's brightest 21-and-under stars, we're keeping our eyes on three other matches.

It's hard to believe that some of today's top pros once had to qualify—and often together.

Top seed Jannik Sinner will meet No. 7 seed Lloyd Harris in the first final-four clash Saturday at the European Open.

“The match was a little bit strange,” the Olympic champion admitted after advancing past Lloyd Harris, 7-6 (6), 6-3, 6-4, on Wednesday at Flushing Meadows.

The South African will play in his first major quarterfinal on Wednesday against Alexander Zverev.

The South African has enjoyed a consistent season that already scored him wins over the likes of Rafael Nadal and Dominic Thiem.

In Toronto, South Africa's Lloyd Harris will try to become just the second player ever to beat Rafael Nadal in back-to-back weeks.

The Spaniard had escaped a three-hour, four-minute thriller against Jack Sock the night before.

How will Naomi Osaka fare against Ajla Tomljanovic in her first match since capturing a fourth major title at the Australian Open? And who will prevail in an all-American meeting between Amanda Anisimova and Sloane Stephens?