Nadal clinches year-end No. 1 ranking in London

London, England ( - For the third time in his brilliant career Rafael Nadal will finish as the ATP's year-end No. 1.

The top-seeded Spanish superstar also secured a berth in the semifinals this week in London by handling seventh-seeded Swiss Stanislas Wawrinka 7-6 (7-5), 7-6 (8-6) in 2 hours, 13 minutes on Day 3 of round-robin action at the $6 million ATP World Tour Finals -- the prestigious eight-player season-ending event at The O2.

Wawrinka tried everything he could to force a third set, as he overcame a 1-4 deficit in the second and a 1-4 deficit in the second-set tiebreak, but a fierce Nadal would not be denied. The fiery Spaniard saved a set point in the tiebreak and converted on his first match point when Wawrinka netted one final forehand.

Nadal improved to 12-0 lifetime against Wawrinka and has never dropped a set against the Swiss slugger (26-0).

Wawrinka fell to 0-15 lifetime against world No. 1 players.

The 27-year-old former Tour Finals runner-up Nadal was also a year-end No. 1 in 2008 and 2010. He also becomes the first player to hold, lose and regain the year-end No. 1 ranking on two occasions. Roger Federer and Ivan Lendl each accomplished the feat once.

"[It is] one of the best things that I did in my career -- come back to the No. 1 after three seasons. That's very difficult in our sport ... [and] that's an emotional thing for me."

Wednesday's round-robin nightcap saw fifth-seeded Tomas Berdych douse last week's Paris Masters runner-up David Ferrer, this week's third seed, 6-4, 6-4, in 83 minutes. Berdych swatted 10 aces and broke serve twice while holding his big serve throughout.

Ferrer beat Berdych in a quarterfinal in Paris last week.

This week's four-player Group A features the U.S. and French Open champion Nadal (2-0), the Roland Garros runner-up Ferrer (0-2), Berdych (1-1), and Wawrinka (1-1).

Group B is comprised of Australian Open titlist Novak Djokovic (1-0), fourth-seeded former U.S. Open champ Juan Martin del Potro (1-0), the 17-time Grand Slam winner and six-time Tour Finals king Federer (0-1), and eighth-seeded Richard Gasquet (0-1).

On Thursday, the second-seeded two-time Tour Finals winner Djokovic will battle the fourth-seeded del Potro and the sixth-seeded Federer will take on Gasquet. Djokovic has won his last 18 matches overall, including a title at last week's Paris Masters.

Djokovic beat Federer in last year's Tour Finals finale here in London.

The red-hot Djokovic and Federer are the only former champions in the field this year. Nadal was the runner-up in 2010; Ferrer was the runner-up in 2007; and del Potro was a runner-up in 2009.

Round-robin play will be staged through Saturday, with the semifinals on Sunday, and the final on Monday. The top-two players from each group will qualify for the semis.

An undefeated champion this week would earn $1.923 million.