Day 4 of the 2012 U.S. Open is underway, as currently No. 12-seeded Ana Ivanovic is in action against Sofia Arvidsson in a second-round match at Arthur Ashe Stadium. Ivanoic leads Arvidsson, 6-2, 5-1, and a victory would send her into the third round.

Other second-round matches in action are: Maria Kirilenko vs. Greta Arn, Galina Voskoboeva vs. Andrea Hlavackova, Dominkika Cibulkov vs. Bojana Jovanovski and Jelena Jankovic vs. Lara Arruabarrena.

Later on, about 2 p.m. ET, No. 4 seeded Serena Williams takes on Maria Jose Martinez Sanchez at Arthur Ashe Stadium. The final women's match of the night will be played between No. 6 Angelique Kerber and Venus Williams.

On the men's side, No. 1 Roger Federer plays a second-round match against Bjorn Phau at 7 p.m. ET. The match will be the

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