World No.1 and top-seed Simona Halep has retired from her first-round contest at the China Open in Beijing due to a back injury.

Romania’s Halep lost the opening set to Tunisian qualifier Ons Jabeur 6-1 in 31 minutes before calling a halt to proceedings.

“There is a pain. I couldn’t move properly, so that’s why I stopped,” Halep said on wtatennis.com.

“It’s really tough when you have back injury because you cannot bend, you cannot react at the balls. I couldn’t play.”

Third seed Angelique Kerber of Germany had no such trouble, defeating France’s Kristina Mladenovic 6-2 6-2, and fourth seeded Caroline Garcia of France beat wildcard Wang Yafan 7-6 (12-10) 6-7 (4/7) 6-3.

Zheng Saisai, another Chinese wildcard, advanced after beating Dayana Yastremska 6-4 6-3.

Daria Kastakina, the 13th seed, was 6-4 4-2 down to Germany’s Laura Siegemund before retiring.

Qualifier Polona Hercog defeated Coco Vandeweghe of the US 6-2 6-1 while Latvia’s Anastasija Sevastova, Lesia Tsurenko of Ukraine, Dominika Cibulkova of Slovakia and USA’s Madison Keys were the day’s other winners.

Australia’s Daria Gavrilova is already through to the second round having stunned world No.5 and two-time Wimbledon winner Petra Kvitova 6-2 6-1 in her opener on Saturday while compatriot Samantha Stousur is due to face Karolina Pliskova in her first match.