Novak Djokovic ATP World Tour Finals World Number One
Novak Djokovic kisses the world number one trophy after defeating Tomas Berdych at the ATP World Tour FinalsReuters

Novak Djokovic ensured he would end another year as world number one while adding another processional victory to a long list at the ATP World Tour Finals with his 6-2, 6-2 demolition of subdued Czech Tomas Berdych on Friday.

The Serb, virtually guaranteed a semifinal berth before walking on court at the O2 Arena, made doubly sure by cruising past Berdych in little more than an hour.

He will meet Japan's Kei Nishikori in Saturday's first semifinal before Roger Federer plays his Swiss compatriot Stanislas Wawrinka in the evening match, following Wawrinka's 6-3, 4-6, 6-3 victory over Marin Cilic on Friday.

A day after Roger Federer dropped only one game beating home favourite Andy Murray to win Group B, Djokovic was also in ruthless mood to top Group A and guarantee ending the year as world number one for the third time.

The Seven-time Grand Slam champion Djokovic has now topped the closing standings for three of the last four years.

"To be able to stand next to this trophy and to have the crown for all the achievements in this 12 months, it's very fulfilling and it's a joy," Djokovic said after being presented with the year-end number one trophy in front of a parade of former world number ones including his coach Boris Becker.

"The tournament is not over. I have maybe a few hours of celebration and then turning back to the semi-finals and preparing for it."

Djokovic's 30th indoor victory in succession since the ATP World Tour Finals in 2012, lined up another meeting with Nishikori after the Japanese debutant finished second in Group B.

After a series of one-sided encounters throughout the week, Berdych's capitulation felt like no great surprise as he slipped 4-0 behind in the opening set against a man playing at a sublime level.

"I think it just shows how great he is, how well he has played during the whole season," Berdych said of Djokovic's confirmation as year-end number one.

Later on Friday, Wawrinka set up a meeting with Federer, his partner in the Davis Cup final for Switzerland next weekend, needing just 12 minutes to win the three games which guaranteed a semi-final place for a second year running.

Fresh from breaking Cilic's serve to move into that 3-1 lead, Wawrinka looked sharp and in no mood to let up, taking the first set in 32 minutes. It looked odds on that an 11th encounter among the 12 round-robin matches would not go beyond two sets.

Instead, the rarity of a proper contest breaking out suddenly materialised when Wawrinka threw in an absent-minded service game at 4-5 in the second set, getting broken to love.

In the decider, Wawrinka, perhaps already thinking ahead to the Federer game, seemed even more distracted as was again immediately broken but he regrouped and broke back, reeling off four straight games to prevail after one hour 45 minutes.

By the end Australian Open champion Wawrinka was playing with some of the panache he will need to earn a rare win over Federer, who leads 14-2 in their head-to-heads, and Cilic finally capitulated with a double fault on the final point.

It was one of the better games of a tournament which has had more than its share of flat spots but the sell-out crowds will be hoping for a couple of closer semifinals with the alluring prospect of a Djokovic-Federer final showdown on Sunday.