Just two months remain of the 2018 ATP World Tour season and there is still a No. 1 spot to be decided.
After last week's final match of Grand Slam tennis where Novak Djokovic claimed his third US Open title against Juan Martin del Potro, there are just a handful of tournaments left on the calendar.
There are just two ATP Masters tournaments remaining where some of the top players will travel to Shanghai before the final ATP regular event of the Paribas Masters takes place in Paris.
There are also ATP 500s and 250s still to be played in the cities of Vienna, Basel and more. Last season saw Rafael Nadal claim the year-end No. 1 title at the ATP World Tour Finals in London.
But can the Spaniard match that achievement once more? Or will another name come and deny that scenario from happening?
Here are your four contenders for the year-end No. 1 ranking...
#4 Juan Martin del Potro
Juan Martin del Potro is one of the most loved tennis players on the ATP circuit as some of his fans like to nickname him the BFG (Big Friendly Giant).
Last week saw the Argentine finish runner-up to Novak Djokovic at the US Open. Del Potro said in an interview that he nearly retired from the sport in 2015 due to his long list of injuries which was mainly on his wrist. Three years on and now he is ranked no. 4 in the world and has an outside chance of finishing the year as world no. 1.
The 2009 US Open champion's next appearance will be at next month's China Open in Beijing where the likes of Nadal and Grigor Dimitrov will also be competing.
Del Potro is currently 2780 points behind Nadal in the ATP rankings so it is a big ask but doable depending on his rival's results.
#3 Novak Djokovic
The second half of the 2018 season has been an impressive one for Novak Djokovic who is starting to show his old self again. Djokovic on his day can be the best in the world with his match dominance against his opponents.
The Serbian showed that at last week's US Open final against Del Potro by beating the Argentine in straight sets.
The last time Djokovic ended an ATP season as the world number No. 1 was back in 2015 where he won 11 titles.
Djokovic is currently 2315 points behind Nadal in the ATP rankings and with two Masters 1000s tournaments remaining, the 31-year-old has a pretty good chance of beating the Spaniard to it.
#2 Roger Federer
Roger Federer is having a mixed second half of the 2018 season.
He started the year defending his Australian Open title against Marin Cilic but failed to retain Wimbledon before finishing runner-up to Djokovic at the Cincinnati Masters.
The Swiss man is currently the world number two but he has the likes of Djokovic and Del Potro to watch over his shoulder. Federer's next tournament on the ATP calendar will be next month's Shanghai Masters with the winner taking home 1000 points.
The 20-time Grand Slam champion knows what it takes to win in Shanghai and will also compete on home soil in Basel later on in October before travelling to Paris for the Paribas Masters.
1860 points separate Federer and Nadal for the top spot and it could well and truly go down between the two come the ATP World Tour Finals.
#1 Rafael Nadal
Rafael Nadal is, of course, an obvious contender for the world number one spot. The Spaniard has spent most of the season so far on top of the men's tennis tree but will he stay there come the end of November when the season wraps up for another year?
His next appearance after this weekend's exhibition of the Laver Cup will be the China Open where he will bid to defend his title.
And if he does that it will be 500 points in the bag.
His main rival for the No. 1 spot, Federer, is competing at the same tournaments apart from the China Open which gives Nadal the opportunity to open up the gap.
Nadal is currently the favourite but he knows not to underestimate the progress Djokovic is showing by winning the last two majors and Federer is Federer, he knows how to win the big tournaments again and again.
Who do you think will end the year world No. 1? Comment below..,
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