The 2012 U.S. Open continues with second-round action from New York Thursday, with Roger Federer and the Williams sisters highlighting action on the fourth day of play.

It's still early, so most of the stars are expected to advance. But Venus Williams is no longer one of those stars: after her struggles with her health and a first-round exit at Wimbledon, she isn't a lock for semifinals major after major anymore. She'll won in straight sets Tuesday, but she'll still be the underdog in a matchup against sixth-seed Angelique Kerber in a primetime matchup Thursday.

Here's the schedule of play from Arthur Ashe Stadium:

Day session (begins at 11 a.m.): Sofia Arvidsson vs. No. 12 Ana Ivanovic

No. 23 Mardy Fish vs. Nikolay Davydenko

Maria Jose Martinez Sanches vs. No. 4 Serena Williams

Night session (begins at 7 p.m.): No. 1.Roger Federer vs. Bjorn Phau

No. 6 Angelique Kerber vs. Venus Williams

Other notables on the fourth day of play include fifth-seeded Jo-Wilfried Tsonga, who will take on Martin Klizan, second-seeded Agnieszka Radawanska, facing Carla Suarez Navarro, and 27th-seeded American Sam Querrey, who will be tested by Ruben Ramirez Hidalgo.

The Tennis Channel will have coverage from 10:30 a.m. to 7 p.m. Thursday, while ESPN2 will carry the tournament from 1 p.m. through the primetime matches until 11 p.m.

For more on the 2012 U.S. Open, please be sure to check out SB Nation's dedicated tennis hub and SBNation.com for all the latest news and updates