Second round singles action begins on Wednesday in New York. And with rain disrupting play on Tuesday, some first round matches are yet to be completed, making for a busy Wednesday.

Day 4 sees defending champions Carlos Alcaraz and Aryna Sabalenka as heavy favorites in their second round matches. Plus, two top Americans who are legitimate contenders for this title face familiar faces. Jessica Pegula plays 2020 Australian Open champion Sofia Kenin, while Ben Shelton takes on fellow Major semifinalist Hubert Hurakcz.

Here’s a rundown of the most notable matches on Day 4 (in chronological order, all times local):

Jessica Pegula (3) vs. Sofia Kenin (WC) – 11:30am on Arthur Ashe Stadium

Pegula has reached the semifinals or better at three of the last four hard court Majors. She comfortably won her opening round, with the loss of five games. Kenin overcame Venus Williams in a match that, quite ridiculously, didn’t even start until after midnight. Pegula leads their head-to-head 4-2, and claimed both of their more recent encounters in straights.

Ben Shelton (8) vs. Hubert Hurkacz – Second on Arthur Ashe Stadium

Shelton recovered from what he described as a nervous first set against Tallon Griekspoor on Monday, which he lost 6-1, to prevail in four. Hurkacz also took his first round in four, as he looks to rebuild his ranking after multiple surgeries the last few years. But he did win a Challenger-level hard court title just a few weeks ago. This is surprisingly the first career meeting between two of the sport’s biggest servers.

Marta Kostyuk (11) vs. Sloane Stephens (WC) – Second on Louis Armstrong Stadium

Kostyuk achieved her first two Major semifinals this year in Paris and London, but the US Open remains the only Major where she’s yet to advance beyond the round of 16. Stephens’ US Open title came nine years ago, and she’s now ranked outside the world’s top 200, having played sporadically of late. Two weeks ago in Cincinnati, Kostyuk defeated Stephens 7-5, 7-5.

Aryna Sabalenka (1) vs. Polina Iatcenko (Q) – Not Before 7:00pm on Arthur Ashe Stadium

It’s been six full years since Sabalenka lost this early at a Major. However, early losses have become more common as the season has progressed, as she’s failed to reach the quarterfinals at her last three events Iatcenko is a 22-year-old qualifier who required nearly three-and-a-half hours to earn her first-ever victory at a Major on Monday.

Rei Sakamoto (Q) vs. Frances Tiafoe (11) – Not Before 7:00pm on Louis Armstrong Stadium

Tiafoe had to stage a comeback from two-sets-to-one down on Monday night against fellow American Martin Damm. Frances is a two-time semifinalist in New York, though it’s now been over a year since he’s achieved a quarterfinal at a Major. Sakamoto is a 20-year-old who ended his fellow Japanese Kei Nishikori’s hopes of qualifying for his last Major, and Sakamoto followed that up by collecting his first match win in the main draw of a Major, in five sets. He’s a tall, powerful player, and owns a huge serve.

Jaime Faria vs. Carlos Alcaraz (2) – Last on Arthur Ashe Stadium

On Monday, Alcaraz made his return from injury, playing his first match in over four months. And he looked pretty sharp considering, beating Roman Safiullin in straights. Faria won a five-setter in his opening round, and the 23-year-old from Portugal is coming off a run to the round of 16 in Cincinnati as a qualifier.

Wednesday’s full Order of Play is here.