Ten days ago, after he lost to Sam Querrey in his opening match at the Paris Masters, Novak Djokovic looked like a man for whom the end of the season could not come soon enough.
There was even talk that the 25-year-old Serb, weighed down by concerns over his father's health and apparently running on empty after a gruelling campaign, might not make it to the start line for this week's Barclays ATP World Tour Finals.
Tomorrow, nevertheless, the world No 1 will take his place in the semi-finals of the year-ending tournament here in London after becoming the first of the eight singles players to complete a clean sweep of his round-robin matches. Djokovic's 6-2, 7-6 victory yesterday over Tomas Berdych left Andy Murray needing to win just one set against Jo-Wilfried Tsonga in last night's final Group A match to book his spot in the last four.
Roger Federer is a certain semi-finalist from Group B, with the last place to be decided by today's concluding round-robin matches.
Djokovic has won his matches here against a background of further worrying reports about his father, Srdjan, who is said to be suffering from an acute respiratory illness. Earlier this week a Serbian source claimed that Srdjan had been flown from Belgrade to a hospital in Germany.
Although Djokovic has been reluctant to discuss the matter he said yesterday that his father was "better" and talked about "good news every day", which "makes me happier, makes me play more relaxed". He added: "Every win means a lot for my family and me, but there are more important things in life and that's health. I guess that's the priority now."
On the court the season is finishing in very different fashion to 12 months ago. Last year Djokovic was a spent force after winning the US Open, which was his tenth title of the year and his third Grand Slam crown of an extraordinary season.
This time he has won autumn titles in Beijing and Shanghai and secured the year-end world No 1 ranking for the second time in a row.
He said it was "very satisfying" to end the year on top of the rankings. "Obviously that serves as an indication of how good the season was for me," he said. "It was very difficult to follow up after 2011 and to expect myself to repeat that."
Djokovic believes he is finishing the season well because he has been more careful with his schedule in a season made busier than ever by the Olympic tournament. He did not play in any Davis Cup ties and competed in just two tournaments (Dubai and Beijing) below Masters Series level. He even skipped the Belgrade event owned by his family.
He said he was still tired at the end of a long season but added: "If you are winning matches, obviously you feel better. But because this is the last tournament of the year for most of the players it is a challenge to find that last drop of energy, physical, mental, to find their best game."
With one tournament to finish Djokovic has won only half as many titles as last year, but has still been hugely impressive. In a year when Murray finally made his Grand Slam breakthrough, when Federer enjoyed a resurgence and when Rafael Nadal continued to dominate on clay, Djokovic has still won one Grand Slam tournament, finished runner-up in two more, was a semi-finalist at Wimbledon and the Olympics and won three Masters Series titles. Two more victories here, moreover, and he will finish the season with his second year-end championships trophy.
Berdych, who can now concentrate on next weekend's Davis Cup final between Czech Republic and Spain, had won only one of his previous 11 matches against Djokovic and was in trouble from the moment the Serb broke in the third game. Returning superbly and striking the ball with great consistency from the back of the court, Djokovic broke again to take the opening set in just 34 minutes.
When Djokovic made his third break in the third game of the second set, it seemed the end would be swift. Berdych, nevertheless, broke back immediately and when he led 6-3 in the tie-break tournament organisers were probably reaching for their calculators to see how his recovery might complicate the qualifying scenario. Djokovic, however, won the next five points and converted his first match point when Berdych hit a return long.
Djokovic was presented with an award as the year-end world No 1 earlier this week but said he was even more honoured to have been named by the Association of Tennis Professionals as the Arthur Ashe Humanitarian of the Year for his work with his foundation, as a UNICEF ambassador and for other charitable ventures. "This is something that makes all the people working in our foundation very happy and motivates us all to do even more," he said.
Saturday match schedule
Singles: Group B
R Federer v J M Del Potro (not before 1.45pm)
D Ferrer v J Tipsarevic (not before 7.15pm)
Doubles: Group A
B Bryan/M Bryan v L Paes/R Stepanek (12pm)
M Granollers/M Lopez v A-u-H
Qureshi/J-J Rojer (not before 5.45pm)