After cruising through the opening set and surrendering the next, Zverev gained a foothold in the see-sawing third ⁠set when he grabbed a 4-2 lead but ‌a sudden spell of rain halted play on ​John Cain Arena and threatened to disrupt the German's rhythm.

With the roof closed and court towelled dry during a near 40-minute break, the third seed got ‌back to work and barely skipped a beat on serve as he comfortably closed out the set to regain control of ⁠the contest.

Zverev broke Muller for a sixth time early in the next set but the three-time Grand Slam runner-up paused at 2-1 and sat down in his chair with what appeared to be a leg problem before the 28-year-old soldiered on after medical treatment.

Some big winners followed from Zverev's racket as ⁠he looked to shorten his time ‌on court, and he squandered two match points before delivering the knockout blow in the form of a big ace to book a meeting with ⁠British 26th seed Cameron Norrie.