UPDATE 2-Tennis-Ill Williams follows seeds out of Wuhan Open

* Top seed Williams quits in first set against Cornet * Second seed Halep loses in three sets to Muguruza (Adds details) Sept 23 (Reuters) - World number one Serena Williams added her name to the list of slain seeds at the Wuhan Open on Tuesday after the American was forced to retire from her second round match against France's Alize Cornet because of illness. The top seed, playing her first match since winning her 18th grand slam singles title at the U.S. Open earlier this month, broke Cornet to lead 6-5 in the first set when she called for the doctor to come on court at the change over. Williams sat solemnly, head down with a towel around her neck and a thermometer in her mouth during the examination before making the quick decision against continuing. The 32-year-old also had her blood pressure checked and walked slowly off court with the help of the trainer, with reports saying she went to hospital for further tests. She had shown flashes of her usual brilliance but looked shy of full fitness throughout her hour of activity on the centre court, with the lengthy 11th game, which included several deuces, proving particularly taxing as she leant on her racquet between points. Her exit only added to the headache for organisers of the inaugural $2.4 million hard court event, where top names tumbled in early action after the city's tennis trailblazer Li Na announced her retirement from the game last week. Former world number one and 10th seed Jelena Jankovic was also forced to quit her second round match on Tuesday in the first set while trailing American CoCo Vandeweghe 4-1. The Serb, suffering a back injury, joined 10 other seeds in failing to make the last 16. They included Romanian world number two Simona Halep, who was beaten by an aggressive display from Garbine Muguruza to kick-off a second day of upsets in China. The Spanish 20-year-old smashed 34 winners as she knocked out the second seed 2-6 6-2 6-3 and set up a third-round meeting with Ukrainian Elina Svitolina, who battled back from a 5-0 first set deficit to edge Germany's Sabine Lisicki 7-6(3) 6-3. Italian 11th seed Sara Errani was ousted by American Alison Riske 6-4 6-4, while Swiss qualifier Timea Bacsinszky defeated 13th seed and U.S. Open semi-finalist Ekaterina Makarova of Russia 6-4 6-1. Danish eighth seed Caroline Wozniacki, who lost to Williams in the Flushing Meadows final in New York, narrowly avoided joining the exodus after battling back from a break down in the third set to edge Spain's Carla Suarez Navarro 6-1 3-6 7-6(4). Wozniacki returned to the centre court later in the day to present twice grand slam winner Li with flowers as the Wuhan resident received warm applause from the crowd. Wimbledon finalist Eugenie Bouchard was another seed pushed all the way in Tuesday's evening session. The Canadian set up a third round clash with Riske after edging Germany's Mona Barthel 4-6 6-3 6-4 in her first match of the tournament. One German who did make it through was seventh seed Angelique Kerber, who also needed three sets to beat Kazakh qualifier Zarina Diyas 4-6 6-2 6-4. Wimbledon champion Petra Kvitova, the highest seed standing at the tournament at third, had a relatively easy outing in the day's last singles match. The Czech world number three brushed past Italian qualifier Karin Knapp 6-3 6-0 in just over an hour. (Writing by Patrick Johnston in Singapore, editing by Sudipto Ganguly)