Third seed Zverev was made to work hard by Gilles Muller, who tired in the decider as the German prevailed 4-6 6-3 6-2.

And Dimitrov was slow to get going before he got the better of Pierre-Hugues Herbert 3-6 6-2 6-4. The Bulgarian remains on course for a quarter-final meeting with sixth seed David Goffin, who defeated Stefanos Tsitsipas 7-6 (7-4) 7-5.

There was one notable casualty as seventh seed Lucas Pouille went down 2-6 6-1 7-6 (7-3) to Mischa Zverev, who set up the possibility of a last-eight clash against his younger brother.