Nadal took over as world No.1 from Novak Djokovic on Monday, more than two years after he last held the position.
That he has done so despite seven months out with knee problems and without winning a single match in two grand slams is testament to his extraordinary season.
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"I thought I would never have the chance to be back there," he said. "I was confident that when I was back I would have the chance to keep competing, keep having chances to play for important tournaments, but I never thought about being back to No.1. I am today."
Nadal also believes his oldest rival Roger Federer will manage to join him at the Barclays ATP World Tour Finals, despite still needing to earn points to book his place. "He's going to qualify," said Nadal. "I am sure of that. He is not going to have a problem. He is a great player and he will be there and fighting for the title."
Richard Gasquet's hopes of qualifying suffered when he was defeated in the first round of the Shanghai Masters. He was beaten 6-3, 6-4 by Canada's Vasek Pospisil, and lies in ninth position in the race to reach London - which would be enough if, as expected, Andy Murray withdraws following back surgery. Jo-Wilfried Tsonga and Milos Raonic, though, are not far behind.