Roger Federer has reclaimed his spot at the top of the tennis world, securing the year-end No. 1 ranking for the fifth time in his career.

The record 15-time Grand Slam champion is now closing in on Pete Sampras' all-time mark of six.

Federer earned the top year-end ranking after winning his opening two matches at the ATP World Tour Finals. Nadal, who ended Federer's five-year run as the end-of-season No. 1 last year, had a mathematical chance of overtaking Federer for the top spot but lost his opening match at the tournament for the top eight players in the world.