Novak Djokovic reveled in his "perfect" five months on Friday as he took aim at his sixth ATP Finals title with the year-end number one ranking in the bag.
Speaking before the start of the season finale at London's O2 Arena, the Serb said next to the Grand Slams and the ATP Finals, reaching the number one spot was the "ultimate challenge" in the sport.
"I'm very proud of that achievement and I understand that it's extra special this year because of the journey I've been through in the last 15 months, especially and particularly in the last eight to 10 months.
"After February's elbow surgery it looked quite improbable that I would be in this position as the year-end number one, not just because of the rankings — I was 22 (in May) — but just because of how I felt on the court, how I was playing.
"It turned to out to be a perfect five months of the year, with two Grand Slam titles," he added.
Djokovic is seeking his fifth ATP Finals title in London to go with his first, which he won in Shanghai in 2008.
If he wins the tournament, which starts on Sunday, he would draw level with Roger Federer with six wins in total.