LONDON - Novak Djokovic was at his imperious best as he sealed the year-end world number one spot and advanced to the semi-finals of the ATP Tour Finals with a 6-2, 6-2 thrashing of Tomas Berdych on Friday. Djokovic finishes on top of the rankings for the third time in four seasons and is only the seventh player to hold first place at the end of the calender year on at least three occasions.

The Serb's third successive victory at the prestigious season-ending event at London's O2 Arena ensured he won Group A and will face Japan's Kei Nishikori in Saturday's semi-finals. "It's been a long year, a long season, it's an incredible achievement and I want to thank my team and my family and all the people who supported me," Djokovic said. "I'm aware that being number one in the world is the biggest challenge a tennis player can have. It's an incredible feeling and I'm very happy. This was definitely one of the best performances. I hoped I could continue the way I played in the first two matches."

The number one ranking is a fitting reward for the Serb's remarkable consistency during a year in which he won Wimbledon, reached the French Open final and claimed five other titles. With top spot wrapped up, Djokovic can focus on becoming the first player to win the Tour Finals three years in a row since Ivan Lendl in the 1980s.

Few would bet against him after he lost a combined nine games during his three majestic group victories. It is the 11th consecutive year that one of Djokovic, Roger Federer and Rafael Nadal has finished on top of the rankings.

On Thursday night, Federer sent Andy Murray crashing out of the ATP Tour Finals in humiliating fashion with 6-0, 6-1 victory that ensured Nishikori would qualify for the semi-finals. Nishikori's 4-6, 6-4, 6-1 win over alternate David Ferrer earlier on Thursday left Murray facing the daunting task of having to beat Federer in straight sets to go through from Group B.

But Murray was routed in only 56 minutes in a defeat which equalled his worst ever result, a 6-1, 6-0 loss against Djokovic in Miami in 2007. Federer, bidding for his seventh Tour Finals title, finished top of the group after winning all three of his matches, and he will be joined in the last four by Nishikori on his maiden appearance in the prestigious season-ending event at London's O2 Arena.

"Clearly I'm very happy to play a good match today. I knew I was qualified so maybe I went in a bit more relaxed," Federer said. "It's not the way I thought it was going to go but there's always next year for Andy." It was a horrible way for Murray to end a disappointing campaign which saw him surrender his Wimbledon title, briefly drop out of the top 10 for the first time in six years and fail to win a tournament until the final weeks of the season.

But he could have no complaints after a lacklustre display was brutally punished by Federer, who becomes the ninth player ever to reach the landmark of 250 career indoor wins.

"I've lost slam finals, which have been very tough. But in terms of the way the match went it was not ideal from my side of the court -- far from it," Murray said. "I can say I'm disappointed with my level. But if I played well he probably still would have won anyway."

Murray had a solid record against Federer, winning 11 of their 22 previous meetings, but the Swiss had won both their matches this year and all three of their past encounters at the Tour Finals. Federer was already through to the semi-finals for the 12th time in 13 attempts, equalling Ivan Lendl's record for last four appearances, and Murray was the latest to fall victim to the 33-year-old's dominance under the O2 dome.