London - Novak Djokovic was at his imperious best as he sealed the year-end world No 1 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.
And, after Federer's brilliant demolition of Andy Murray for the loss of only one game on Thursday, it was Djokovic's turn to showcase the current gap that exists between the big three and the rest of their rivals.- Simply untouchable -
The 27-year-old had looked untouchable in his routs of Marin Cilic and Stan Wawrinka and he continued to dominate against Berdych, who had lost 16 of his 18 meetings with the Serb.
Berdych's power serve is his main weapon but the slow pace of the court at the O2 Arena has neutralised many of the big hitters this week and it was no different this time as Djokovic broke without dropping a point in the opening game.
Djokovic's remarkably agile movement when forced to defend meant there was no chance of Berdych out-hitting him from the baseline and the Czech was soon left shaking his head in frustration as he was broken again.
Although the world number seven finally got on the scoreboard after losing the first four games, it was too late to stop Djokovic clinching the set and with it his place in the last four.
As a former Wimbledon finalist, Berdych is hardly a no-hoper, but he was unable to stem the tide and Djokovic broke again in the opening game of the second set.
Another break in the third game effectively ended the contest and it wasn't long before Djokovic was celebrating his 30th successive win in indoor matches with a triumphant group hug with coach Boris Becker and his backroom staff.
Berdych is likely to be eliminated after losing two of his three group matches, but the Czech will have to wait until Wawrinka's meeting with Cilic later on Friday to confirm his fate.