Grigor Dimitrov through as Aljaz Bedene retires with knee injury

The Bulgarian third seed won 7-6 (8-6) 7-5 in Beijing to set up a meeting with Spain's Roberto Bautista Agut.

Former US Open champion Del Potro, a wildcard here, served for the second set but a series of forehand errors gave Dimitrov the decisive break.

British number three Aljaz Bedene retired from his last-16 match against Bautista Agut with a knee injury.

The 28-year-old, ranked 50th in the world, lost the first set 6-0 to the fifth seed, and was trailing 4-0 in the second when he decided not to continue.

Elsewhere, Australian eighth seed Nick Kyrgios beat Germany's Mischa Zverev 3-6 6-2 6-2 in 82 minutes.

Kyrgios received a warning from the umpire after smashing his racquet at the end of the first set, but quickly recovered his composure. He struck 11 aces and converted all four break point opportunities to beat Zverev and reach the quarter-finals, where he will face Belgian qualifier Steve Darcis, who beat Dusan Lajovic 6-3 6-4.