Novak Djokovic's cap causes a stir during victory over Hubert Hurkacz

Novak Djokovic passed his first real test at Wimbledon, but only after he fell foul of the dress code.

The defending champion dropped a set for the first time at the Championships to big-hitting Pole Hubert Hurkacz, 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 strict 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 was against the rules.

"In the last match I was starting to unpack my hat," said Djokovic. "The chair umpire said he needs to check whether or not I'm able to play with it.

"He got a confirmation that I was able to play. So I got the permission. I played with the hat.

"The same hat I took out now, I was not able to play with it. That's why I was just questioning that call.

"I mean, no one has approached me before the match to tell me, 'well, you can't really play with the hat this match'. That's all.

"I don't play always with a hat. It depends on whether it's sunny, whether I need it, hot, angle of the sun, whatever it is."

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.