LONDON (REUTERS) - Tennis' world No. 1 Novak Djokovic will bid for a record fourth successive ATP World Tour Finals crown in London later this year after becoming the first man to qualify for the season-ender.

Five-time Australian Open champion Djokovic reached the French Open semi-finals by crushing Rafa Nadal on Wednesday and has been virtually unbeatable this season and is currently on a 27-match unbeaten run.

The 28-year-old Serb is looking to become the eighth man in history to complete a career grand slam by winning the French Open this week.

Djokovic won the elite ATP Tour Finals for the first time in Shanghai in 2008 and has a hat-trick of titles in London, last year gaining a walkover against injured Roger Federer.

"I had a great start to 2015 so I am really happy to have qualified so early. I hope I will have a great finish to the year too; I love playing at the O2," Djokovic said.

London's O2 Arena has hosted the event since 2009.