Nishikori's goal: Break into Top 4, and then chase Djokovic and Murray

Kei Nishikori is aiming to break into the Top 4, and then start chasing Andy Murray and Novak Djokovic in the rankings.

Nishikori is currently No. 5—he reached No. 4 in 2015—but he’s just 345 points behind fourth-ranked Milos Raonic and 410 points behind third-ranked Stan Wawrinka. Nishikori defeated Wawrinka, 6-2, 6-3, in round-robin play at the ATP World Tour Finals on Monday.

"I'm not thinking too much about rankings, but [it] would be nice if I could finish No. 4 or No. 3," he said after the win. "I see [a] good chance to be there if I can play good this week. That's one of my [goals] this week."

The Japanese baseliner, 26, got injured in Tokyo but said he put in a strong week-and-a-half of practice coming into the Tour Finals.

Next season, he will look to "stay No. 4 or No. 3" and aim to "catch up [with] Andy and Djoko."

Raonic, who is in the other round-robin group, also won his first match at the ATP Tour Finals, defeating Gael Monfils, 6-3, 6-4.

Nishikori will play Murray in London on Wednesday.