Naomi Osaka was forced to retire from her China Open meeting with Coco Gauff due to a lower back injury, sending the American through to the quarter-finals.

Osaka, who was aiming for her fourth successive win after returning from maternity leave, had earlier caused Gauff plenty of problems as she took the opening set.

After a series of breaks to open the match, Osaka went into the changeover 3-2 up but received treatment on her back after appearing to struggle with her movement.

Some error-prone play by Gauff allowed Osaka to clinch a third break before serving out the opener, but she swiftly gave up a break to go behind in the second set.

Gauff ultimately edged a hard-fought, 51-minute second set featuring several more breaks, with Osaka retiring before the decider could get underway, having struggled to land her first serves in the latter stages.

Gauff now advances to the China Open quarter-finals for the second year in a row, with Ukraine's Yulia Starodubtsewa up next for the world number six.

Fellow American and second seed Jessica Pegula, meanwhile, was beaten in straight sets by Paula Badosa, who will face home favourite Zhang Shuai in the last eight.

Data Debrief: Twenty up for Gauff

The victory may not have come in the manner she envisaged, but Gauff has brought up her 20th career win over a former grand slam champion on the WTA Tour.

Since 2000, Gauff is the fifth player to achieve 20 such wins before turning 21, along with Maria Sharapova, Kim Clijsters (28 each), Martina Hingis (24) and Serena Williams (22).