|Australian Open 2019|
|Venue: Melbourne Park Dates: 14-27 January|
|Coverage: Daily live commentaries on the BBC Sport website, listen to Tennis Breakfast daily from 07:00 GMT on BBC Radio 5 live sports extra and watch highlights on BBC TV and online from 19 January.|
Novak Djokovic dropped his first set of the Australian Open after becoming frustrated that the floodlights were turned on during his daytime win over Canadian Denis Shapovalov.
The Serb clinched a 6-3 6-4 4-6 6-0 win over the 19-year-old to book his spot in the last 16 and cement his place at the top of the world rankings.
"There was no sense to turn the lights on when we have another four hours of daylight," Djokovic said.
"It was completely unnecessary."
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Djokovic had led by two sets and 4-1 in the third before Shapovalov, 19, won five games in a row to go into a fourth set.
But the 14-time Grand Slam winner quickly reasserted control, wrapping up the final set in just 26 minutes.
Djokovic, who regained the top ranking in November, was guaranteed to retain the position ahead of Rafael Nadal by reaching the last 16 in Melbourne.
The six-time champion is aiming to move clear of Roy Emerson and Roger Federer in terms of all-time triumphs with another win at Melbourne Park next Sunday.
He will play Russian 15th seed Daniil Medvedev in the last 16.
Like Shapovalov, 22-year-old Medvedev is another of the game's rising stars and he will be competing in his first Grand Slam fourth-round match.
He beat Belgian 21st seed David Goffin 6-2 7-6 (7-3) 6-3 to reach the second week without dropping a set
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Lights darken Djokovic's mood
Djokovic had produced a superb all-round display to lead by two sets and a break after an hour and a half - with a straight-forward victory looking a formality.
Shapovalov, seeded 25th, had struggled to cope with the occasion of facing Djokovic for the first time, making 40 unforced errors and facing seven break points up to that stage.
However, the match took an unexpected twist when Djokovic's game suddenly crumbled.
The Serb had become distracted at the start of the set by the Rod Laver Arena floodlights being turned on - despite glaring sunshine still streaming on to the court at about 5:15pm local time - and asked for them to be switched off.
Although he moved into a 4-1 lead, he still seemed slightly unsettled and Shapovalov took full advantage.
"Did you guys see the balls well?" he asked the crowd afterwards.
"I saw them well too," he said to a huge cheer. "It was completely unnecessary to turn on the lights.
"The explanation I got was for TV reasons. I hope the viewers enjoyed it."
Djokovic's mood darkened further when he was given a time violation before the first of three break points at 4-4, saving two before a double fault left Shapovalov to successfully serve out the set.
The Serb took a brief break off court and it enabled him to return refocused.
He set the tone by breaking in the first game, going on to lose just 11 points - including two match points - before another double fault from Shapovalov ended the match.
"I just tried to weather the storm," Djokovic said.
"Denis played well and I made unforced errors to let him back in the match.
"He showed his quality and why we will see a lot of him in the future."