Novak Djokovic continued his quest to win a record seventh Australian Open title by reaching the quarter-finals with a battling defeat of Daniil Medvedev.

The tireless world number one, attempting to become the first man to win the tournament more than six times, fought his way to a 6-4 6-7 (5-7) 6-2 6-3 victory at Rod Laver Arena. 

Medvedev stated that Djokovic is not the player he used to be ahead of the fourth-round contest and might have been regretting those comments as the top seed made him toil for large spells of a match which finished in the early hours of Tuesday morning.

The 15th seed from Russia had not dropped a set en route to the last 16 and put up a good fight, but Djokovic ground down him down to set up a last-eight encounter with Kei Nishikori.

Djokovic bossed the majority of the longer rallies, his incredible fitness levels shining through yet again as he stayed on course for a third consecutive grand slam title - and the 15th of his career.

The Wimbledon and US Open champion showed frustration with the crowd early on but saved a break point by winning a high-quality rally with a cushioned backhand volley at the net and claimed the first break in the next game to lead 4-2.

Medvedev got back on serve at 5-4 when Djokovic dumped a backhand into the net, but the Serb was dictating the longer rallies and wrapped up the set with a backhand winner after a double fault from the 22-year-old.

Djokovic continued to work his exhausted-looking opponent from side to side as he charged into a 5-1 lead in the second set, but the former thrashed a ball in fury after being pegged back at 4-4.

Medvedev maintained his momentum in the tie-break, putting away an easy passing shot after a Djokovic forehand bounced up off the net cord and drawing level when the flustered favourite thudded a forehand into the net.

Djokovic suffered a fall early in the third but picked himself up to regain the upper hand after fending off a break point, going 3-2 up when his opponent sprayed a backhand wide and winning four games in a row to take the set.

Both players tired as the clock ticked past midnight, but Djokovic had enough left in the tank to avoid going the distance, breaking twice in a fourth set he ended with a forehand winner to go through.

STATISTICAL BREAKDOWN
Djokovic [1] bt Medvedev [15] 6-4 6-7 {5-7] 6-2 6-3

WINNERS/UNFORCED ERRORS
Djokovic – 43/50
Medvedev - 38/49

ACES/DOUBLE FAULTS
Djokovic - 6/5
Medvedev - 18/6

BREAK POINTS WON
Djokovic - 7/18
Medvedev - 2/9

FIRST SERVE PERCENTAGE
Djokovic - 67
Medvedev - 65

PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Djokovic - 73/50
Medvedev - 70/35

TOTAL POINTS
Djokovic - 142
Medvedev - 126