Novak Djokovic will almost certainly finish the year at the top of the ATP world rankings for a joint-record sixth time after he claimed a hard-fought win over Borna Coric at the Vienna Open. 

Djokovic needed to win just two matches in Austria to guarantee he will end the year as world number one, unless Rafael Nadal takes up an unlikely wildcard for the Sofia Open. 

After defeating Filip Krajinovic in the first round, Djokovic took a vital step towards cementing his name in the record books with a 7-6 (13-11) 6-3 victory over Coric on Wednesday. 

Pete Sampras is the only previous player to have claimed the year-end number one spot on six occasions, doing so between 1993 and 1998. 

Djokovic is tied with fellow modern greats Rodger Federer and Nadal, who the Serbian lost to in the French Open earlier in October, and Jimmy Connors, but is now set to nose ahead of his rivals, having previously secured top spot in 2011, 2012, 2014, 2015 and 2018. 

His latest win did not come easy, though, with the 33-year-old made to work by world number 24 Coric. 

The pair traded blows in an epic opening set which lasted just under two hours – Djokovic eventually coming out on top in a thrilling tie-break after Coric dropped serve for a third time. 

A first break in set two handed Djokovic the advantage and he then held his nerve to take the eighth game with some wonderful shots in an exhilarating rally, making it 5-3. 

Djokovic's sublime volley close to the net set the tone in the next game and while Coric saved two match points, it was only a case of delaying the inevitable.

Earlier, Stefanos Tsitsipas opted to switch his shoe in the third set of his match with Jan-Lennard Struff, though the third seed ultimately came through the contest to tee up a tie with Grigor Dimitrov. 

With the third set tied at 1-1, Nitto ATP Finals champion Tsitsipas changed his footwear and subsequently broke serve, going on to record a 6-7 (7-3) 6-3 6-4 triumph. 

Daniil Medvedev, meanwhile, is enjoying the hospitality in Austria as he eased past Jason Jung 6-3 6-1 in his first-round match. 

"It's great. The hotel is good, the food is amazing, maybe the best of the year," said the world number six. 

"These small things make tennis players happy all the time. The most important is to play good on the tennis court, so the organisation is very good."