Britain's Andy Murray says overtaking Novak Djokovic as the world's top-ranked player is a big motivation for him for the rest of the 2016 season.
The Serb's mixed form this year means Murray, 29, has a chance to claim top spot for the first time in his career.
On Wednesday, Djokovic pulled out of next week's China Open in Beijing with an elbow injury.
"Trying to reach number one is a goal," said Murray, who plays Italy's world number 94 Andreas Seppi in round one.
"I've never been [top]. It's something I would like to do for the first time, which is maybe more of a motivation for me than some of the guys that have been there before.
"But I want to just try and finish this year strong from a personal point of view. It's been my best season to date, and I want to try to finish it as best as I can."
World number two Murray, who is 4,695 points behind Djokovic in the current world rankings, has had to overcome a thigh strain - picked up on Davis Cup duty last month - but will look for only his fourth ATP title of the season when he faces Seppi on Tuesday.
"I needed to take quite a few days off after the Davis Cup to try and let my injury heal and to rest," added the Scot. "I needed a break anyway.
"I haven't been able to practise as much as usual coming into an event like this. But I feel healthy. My leg feels good."
While Murray has triumphed at Wimbledon and the Olympics this year, Djokovic's form has dipped since beating his rival to the French Open title.
The Serb exited Wimbledon and Rio 2016 in the early rounds, and though he reached the US Open final earlier this month, he was beaten by Switzerland's Stan Wawrinka.