Simona Halep was forced out of the 2018 China Open on Sunday when she had to retire in her match with Ons Jabeur in Beijing.

The world No. 1 retired through injury after losing the first set of her first-round match 6-1 in 31 minutes.

Angelique Kerber and defending champion Caroline Garcia are through, however, after they beat Kristina Mladenovic and Yafan Wang, respectively.

Here's a selection of the day's results, courtesy of the WTA's official website:

Ons Jabeur bt. (1) Simona Halep, 6-1 (ret)

(3) Angelique Kerber bt. Kristina Mladenovic, 6-2, 6-2

(4) Caroline Garcia bt. Yafan Wang, 7-6 (10), 6-7 (4), 6-3

(9) Sloane Stephens bt. Anastasia Payluchenkova, 6-7 (10), 6-4, 6-4

(17) Madison Keys bt. Bernarda Pera, 6-3, 6-4

Halep's injury initially affected her at the Wuhan Open earlier in the month, and she confirmed after her match on Sunday that she will undergo a scan to determine the problem:

Meanwhile, Sloane Stephens produced an impressive comeback to pick up her first win in Asia in 2015, after she lost the opening set to Anastasia Pavlyuchenkova.

The American's victory in the second and third sets was all the more impressive given the manner in which she lost the first.

Per Record's Jose Morgado, Stephens cut a forlorn figure when Pavlyuchenkova took the tiebreak:

Garcia had to dig deep in her match, too, after Wang made her work for her victory.

The Frenchwoman eventually claimed the first set after a mammoth tiebreaker, but the Chinese hit back in the second set:

Garcia's quality told in the decisive third set, though, ultimately winning it comfortably.

Despite serving five double-faults, Kerber had a much more straightforward time in her clash with Mladenovic.

The German broke her four times across the two sets, mirroring the pair's first ever meeting which also ended in a 6-2, 6-2 victory for Kerber.

On Monday, Caroline Wozniacki and Karolina Pliskova will be in action as the first round continues, while in the men's draw Kyle Edmund and Borna Coric are among those set to feature.