Novak Djokovic negotiated big-hitter Hubert Hurkacz to reach the fourth round at Wimbledon.

The defending champion dropped a set for the first time at the Championships to the 6ft 5in Pole, losing a tie-break in the second.

It proved only a minor inconvenience, though, as the four-time winner surged through 7-5 6-7 (5) 6-1 6-4.

The only problem Djokovic faced in the first set was being told he could not wear his cap by the umpire because it contravened Wimbledon's all-white rule.

It would be hard to find a whiter cap, frankly, and Djokovic had worn it during his second-round match, but apparently the black inner lining violated the strict dress code.

Djokovic duly played on cap-less and Court One was a server's paradise until the Serb made the breakthrough in the 11th game, Hurkacz saving three break points but succumbing to a fourth.

Hurkacz was not going to go away quietly, though, and he fashioned two break points at 6-5 in the second, one with a Boris Becker-esque dive volley at the net.

Djokovic repelled both to force the tie-break, but another spectacular volley from Hurkacz helped him level the match.

Stung into action, 15-time grand-slam winner Djokovic broke to love twice as he raced away with the third.

A single break in the fourth was enough to wrap up proceedings, the 32-year-old coming through a decent test to safely make week two.