Rafael Nadal repeated his US Open final triumph with a 7-5 6-2 victory over Novak Djokovic to move to the brink of qualification for the semi-finals at the ATP World Tour Finals in London.
The Spaniard edged a titanic first set that saw Djokovic troubled by a contact lens problem, but the second was much more routine as the world No.1 wrapped up victory in one hour 52 minutes.
Tomas Berdych's victory over Andy Roddick earlier meant Nadal could not secure qualification for the last four, but he is certainly in pole position, while the Spaniard's win means Roddick is still alive in Group A despite two defeats.
Nadal, who did not win a set during last year's tournament at the O2, said: "It was a very good match for me. I was very sorry for Novak for what happened with his eye, I hope he is okay. It was my best match in this tournament."
As he had against Roddick in his first match on Monday, Nadal made a shaky start, giving up a break point in his first service game, but Djokovic was unable to take it, and it was a miss he was made to regret as the world No.1 quickly found his form.
The breakthrough came in the fifth game. Twice Nadal mistimed shots on break points but on the third he seized his chance, scrambling for a Djokovic drop shot and then anticipating the Serbian's follow-up.
Prior to the US Open final, Nadal had lost three times in a row to his opponent, including in straight sets at the same stage of this tournament 12 months ago.
The Spaniard has looked a different player after his superb season, though, so it was something of a surprise when he immediately gave up his advantage with a tame backhand.
Nadal had a chance for another break in the following game but this time Djokovic held firm.
The third seed's evening was about to take an unwelcome turn, though, as problems with a contact lens forced him into an unscheduled break.
He returned to the court but in the 10th game Djokovic found himself facing two more break points, and this time an overcooked backhand gave Nadal the chance to serve for the set.
It quickly became clear Djokovic was still having trouble with his vision, and he shot a despairing glance at his box.
The 23-year-old still managed to earn two break points but he could not take them and Nadal clinched the set when Djokovic drilled a return into the net.
The first set had taken the same amount of time as Roger Federer's demolition of Andy Murray but it soon became clear the second set would not be a repeat.
The contact lens issues seemed to be affecting Djokovic's head as well as his eyes and he meekly surrendered his serve twice to trail 4-0 - making it seven games in a row for Nadal.
The world No.3 did at least stop the rot but it was far too late to change the outcome.