Ivanovic beats Pironkova to reach US Open quarters

Serbia's Ana Ivanovic reacts during her match against Bulgaria's Tsvetana Pironkova in the fourth round of play at the 2012 US Open tennis tournament, Monday, Sept. 3, 2012, in New York. (AP Photo/Kathy Willens)

NEW YORK (AP) — More than four years after her French Open title, Ana Ivanovic is finally back in a Grand Slam quarterfinal.

Roger Federer is headed to his 34th consecutive quarterfinal at a major tournament — by walkover after Mardy Fish pulled out of their fourth-round match at the U.S. Open on Monday because of unspecified "health concerns."

Fish missed about two months this season because of an accelerated heartbeat and had a medical procedure in May. The 30-year-old American's third-round match against Gilles Simon went five sets, lasting more than 3 hours and ending after 1 a.m. Sunday.

Afterward, the 23rd-seeded Fish did not appear at a news conference. Tournament officials said he was getting treatment, but didn't give specifics.

The 12th-seeded Ivanovic beat Tsvetana Pironkova 6-0, 6-4 in the fourth round. Ranked No. 1 in the world in 2008, the Serb has struggled with injuries and her confidence since.

After failing to serve out the match at 5-3 in the second set, Ivanovic broke the 55th-ranked Bulgarian at love in the next game to clinch the victory.

Pironkova, a 2010 Wimbledon semifinalist, went up a break twice in the second set only for Ivanovic to immediately break back. There were seven service breaks in 10 games in the set.

Pironkova held serve just once in the match. Ivanovic had more success on Pironkova's first serve than her own; the Serb won 65 percent of the points when her opponent got in her first serve, compared with 61 percent when her own first serve landed in.

Ivanovic could next face Serena Williams, who plays 82nd-ranked Andrea Hlavackova later Monday.

Federer will meet sixth-seeded Tomas Berdych, who beat 11th-seeded Nicolas Almagro 7-6 (4), 6-4, 6-1.