TWELVE months ago Roger Federer handed Novak Djokovic a walkover at this venue. Last night he trampled all over him. One of the most impressive winning runs in world sport shuddered to a halt under the lights at the o2 last night as the Serb went down 7-5, 6-2 to lose a match at the ATP World Tour finals for the first time since being upset by his countryman Janko Tipsarevic back in 2011. His sixth defeat of an imperious calendar year snapped a winning run of 38 matches indoors, and 23 on all surfaces, stretching back to another Federer defeat, in the final of Cincinnati. Federer's win also means that Andy Murray still has one more match to win before he is secure as the year-end World No 2 for the first time in his career.

As tough a loss as this was for the Serbian, the chances of Djokovic having the last laugh this week should not be entirely discounted just yet. Assuming he can take care of an all-but eliminated Tomas Berdych in straightforward fashion, it would hardly be the biggest surprise if these two men were back here on Sunday for their seventh final of the season, though much would have to change if there was to be a different outcome.

A number of one-sided matches and the odd empty seat or two had led some to wonder whether the ATP World Tour Finals was losing its lustre, but this was more like it. This spectacular arena was rammed as the World No 1 and No 3 slugged it out in the 43rd meeting of the longest-running series, with the Serb attempting and ultimately failing to gain ascendancy in the personal head-to-head between the two men for the very first time in just shy of a decade of play. Where once there was a bona fide loathing between the two men, now it is merely a simmering rivalry, Federer knowing he has the game to hurt Djokovic, but falling short in successive Wimbledon finals.

"It was a special night for tennis and a cool atmosphere," said Federer, who sensed his opponent's weakness and went in for the kill like a big game hunter. "You guys made it really nice for us."

Nice for him, he might have said. Both men have enviable skill sets, but Federer had this crowd eating out of his hand. By contrast, every one of Djokovic's uncharacteristic 22 unforced errors in the course of the match were rather uncharitably cheered to the rooftops. "I won't tell you the tactics which worked because we might play again," added the Swiss, who is sporting some designer stubble in London this year. "I did play very well and regardless of the tactics, it is indoors so aggressive tactics pay off. The beard always grows differently here in London. I shaved this morning and it is back this afternoon."

Such celebration seemed a lifetime away when the Swiss was break point down in the opening game, but Federer served his way out of trouble - he racked up an impressive six aces - and made more inroads into the Djokovic serve the longer this one went on. He took the set with an immaculate half volleyed drop shot which landed on the line, finally breaking some stout Serbian defence.

Federer, who guarantees his semi-final place with this win, rode his momentum to establish an early 2-0 second set lead, then squandered it again for 2-2. But Djokovic was strangely out of his comfort zone and the 34-year-old, the second oldest man ever to qualify for this event, was wily enough to sense it. Two more service breaks followed, the first match point saved by the Serb after a sensational 25-shot rally, before Hawk-Eye confirmed that one last Djokovic forehand was into the tramlines and Federer had a precious victory. What he would give to have another one, quite possibly against the same man, come Sunday.

"You have those days as well when you are not feeling your best, not even close to the best," said Djokovic. "Credit to Roger for mixing up the pace. But I made a lot of,unforced errors. I just handed him the win, especially in the second set. I need to now reflect on the things I've done wrong, why this happened, and keep moving forward. This is the last week of the year. Obviously it's been a long season. But I need to push myself mentally, physically, emotionally as far as I can." Federer now faces Kei Nishikori, who overcame Berdych by 7-5, 3-6, 6-3 scoreline earlier in the day.