Group B outsider Robin Soderling is within sight of a place in the Barclays ATP World Tour semi-finals after following up his victory over Rafael Nadal with a 7-6 (7/5) 6-1 defeat of defending champion Novak Djokovic at London's O2 Arena this afternoon.
The Swede only qualified for the tournament as a reserve after Andy Roddick pulled out injured but his progression will be confirmed if Nadal beats Nikolay Davydenko tonight.
Ahead of the match, Roger Federer was presented with a trophy by ATP chairman Adam Helfant after he clinched the year-end number one ranking with his victory over Andy Murray last night.
That match was played in a raucous atmosphere at a packed O2 and it was inevitable this afternoon's clash would be a more sedate affair, although the attendance was still impressive.
Soderling had played exceptionally well in his win over Nadal on Monday, with his bullet forehand proving particularly troublesome for the world number two, but it was more hit and miss in the early stages today.
The Swede needed four huge serves to avoid being broken in the third game but he was then presented with a golden opportunity to clinch the first set in game 10.
Twice Nadal had faltered at 4-5 against Soderling and it looked like history would repeat itself only for Djokovic to recover from 0-40 - a mammoth rally at deuce finding the world number nine unable to break his opponent's resistance - to hold.
Into the tie-break they went and there were mini-breaks aplenty before Djokovic finally succumbed to his opponent's power to go down 7-5.
The world number three had beaten Soderling in all five of their previous meetings, including in Paris two weeks ago in a result that looked like denying the Swede a place in the end-of-season tournament.
Indeed, Djokovic came into the event as arguably the man to beat after back-to-back titles in Basle and Paris but he has also had the heaviest schedule of the top contenders this year and a three-set epic against Nikolay Davydenko on Monday night did not help.
The 22-year-old admitted afterwards he was running on empty and his task became even harder when he was broken in the third game of the second set, Djokovic failing with an attempted drop shot at the end of a titanic rally.
The Serbian looked resigned to his fate and he tamely surrendered his serve for a second successive game as Soderling, who by now was playing very well, surged into a 4-1 lead.
Djokovic battled hard in an attempt to least force his opponent to serve out for victory, saving one match point with a backhand winner, but a netted volley sealed his fate.
Soderling said: "I played a very good match today. I didn't start that great but my serve helped and after seven or eight games I started to play better and better, and it's just great."