Eight months ago, when the Australian Open became the latest in a string of tournaments he had missed through injury, there were those who wondered whether Rafael Nadal would ever play again.
Tonight, the 27-year-old Spaniard faces Novak Djokovic in the US Open final to extend one of the most remarkable sequences in the history of the modern game.
Since making his comeback after seven months on the sidelines nursing yet another knee injury, Nadal has played in 13 tournaments, reached 12 finals and suffered only three defeats – to Horacio Zeballos in the final of his first comeback tournament in Chile, to Djokovic in the Monte Carlo Masters final on his first reappearance in Europe, and to Steve Darcis in the first round at Wimbledon, where he was clearly in no condition to play.
Astonishingly, the world No 2 has won all 21 matches he has played this year on hard courts, traditionally his most challenging surface.
Although he cannot reclaim the world No 1 ranking from Djokovic tonight, he seems certain to do so at some stage in the last two months of the season.
No wonder Djokovic described facing Nadal as the biggest challenge in tennis. "He's the ultimate competitor out there," Djokovic said on Saturday night in the wake of his own gruelling semi-final victory over Stanislas Wawrinka.
"He's fighting for every ball and he's playing probably the best tennis that he ever played on hard courts. He hasn't lost a match on a hard court this year, and we all knew that over the course of the last six or eight years, hard courts haven't been his favourite surface.
"He has had many injuries on this surface, but now he looks fit. He had seven months off. He's lost three matches this year. Without doubt at the moment he's the best player this year – no question about it," Djokovic said.
While Djokovic needed more than four hours to beat Wawrinka 2-6, 7-6, 3-6, 6-3, 6-4, Nadal brushed aside Richard Gasquet 6-4, 7-6, 6-2.
It was the Frenchman's 11th defeat in a row to Nadal, though he had the consolation of becoming the first player to break the Spaniard's serve at this tournament.
Djokovic admitted that Wawrinka, who beat Andy Murray in the quarter-finals, had been the better player for much of their match, but the 26-year-old Serb showed all his fighting qualities, especially after the Swiss had held his serve to lead 2-1 in the deciding set after an extraordinary 21-minute game which featured 12 deuces.
While Nadal has won 21 of his 36 matches against Djokovic, the French Open champion has lost three of their five Grand Slam finals and 11 of their last 18 meetings.
The two men have had some epic battles, including last year's Australian Open final, which was the longest in Grand Slam history, Djokovic winning after five hours and 53 minutes.
Today will be their third meeting in the US Open final in the last four years.
"The way he's been playing he's very confident, but I know how to play him," Djokovic said.
"Hard courts are my most successful surface. I have already played him twice here in the final. I know what I need to do."
When Nadal was asked if he liked playing Djokovic, he smiled. "I prefer playing someone else," he said.
"I'd rather play someone I have a better chance of beating.
"We've played a lot of times and we've played some very exciting matches. When you are involved in these kind of matches you feel special. At the end, even if I lost that final in Australia, I felt happy to be involved."