Novak Djokovic, who has had a tough time lately, insists he is at peace with himself as the season draws to an intriguing climax in London this week. However, he betrayed uncharacteristic tetchiness when asked if he thought smashing a ball into the crowd at the O 2 Arena in Greenwich on Sunday might have injured a spectator – and if it also indicated something about his “mindset” towards the end of what had begun as a season full of promise for him and has ended in one of rare struggle.

Djokovic’s Spanish life coach, Pepe Imaz, who was a vision of serenity sitting courtside – not far from his tennis coach, Boris Becker – might have some work to do yet. The player says he has for several years sought guidance from Imaz, a former fringe player on the Tour. He turned to him again recently when “off court issues”, as he described them at the Rio Olympics, compounded a run of injuries that have bedevilled the latter part of an otherwise outstanding season and contributed to his losing his world No1 ranking to Andy Murray in Paris last weekend.

If he wins every match at the Barclay’s ATP World Tour Finals here this week, he will be No1 again. If surrendering the crown after a run of 123 weeks is the cause of his impatience, it is understandable and perhaps beneficial to his cause. Djokovic is the fiercest of competitors. Losing his composure occasionally ought not to be a major crime; Murray, after all, has built a career on venting his spleen.

In the opening singles, however, Djokovic was warned for unsportsmanlike conduct when he belted the ball roughly in the direction of his box after losing the first set to the promising young Austrian Dominic Thiem, before going on to win 6-7, 6-0, 6-2 in convincing style.

Towards the end of what had been an amicable press conference, this is how the exchange unfolded:

Questioner: “Back to the end of the first set, we saw you similarly venting your frustration at Roland Garros, throwing your racket. Does it concern you one day that will cost you dearly? If it hit someone...”

Djokovic: “You guys are unbelievable.”

Q “Why is it unbelievable?”

ND “Because you’re always picking these kind of things.”

Q “If you keep doing these things ...”

ND “I keep doing these things? Why don’t you get suspended then?”

Q “You were close, weren’t you?”

ND “I’m close? I’m still not suspended, so if I’m not close, I’m not close.”

Q “If that ball had hit a spectator, it could have been serious.”

ND “It could have been, yes. It could have snowed in the O 2 Arena, as well, but it didn’t.”

Q “You’re not concerned about your mindset?”

ND “I’m the only player that shows his frustration on the court? That’s what you are saying?”

Q “You’re one of the top-ranked players in the world.”

ND “So?”

Q “You are showing this frustration. I’m asking you, do you think it’s an issue for you?”

ND “It is not an issue for me. It’s not the first time I did it.”

Nor is it. Early in the final of the Rome Masters this year, which he lost to Murray, Djokovic let the racket slip from his grasp and it flew, quite by accident, into the crowd.

No harm was done and he did not seem unduly troubled. Towards the end of that match, though, he complained loudly to the chair umpire about the dangerous conditions of the sodden clay – and, while he had a point, it was clear he was not his usual, controlled self.

All that said, Djokovic played some superb tennis to open his campaign here on his tenth appearance in the finals. He cut his right thumb in the third game, which he held for a 2-1 lead, then hadthe offending digit bandaged on the changeover. That might have briefly disturbed his equanimity – as foot blisters appeared to do when he lost the US Open final to Stan Wawrinka – but it was not immediately apparent.

There was little in the first set, which hit no great heights before the tie-break, and Djokovic saved six of seven set points.

Then, after more than an hour’s struggle, the five-times champion found the killing rhythm that has destroyed so many opponents in nine previous appearances, bagelling Thiem in much the same manner in which he had also nilled Wawrinka and Kei Nishikori in the past.

His pin-point ground strokes dazzled his now ragged opponent, who was playing his 80th singles match of the season but making his debut in the ATP’s showcase finale.

Apart from the controversy and the subsequent blow-up, Djokovic was rightly pleased with his performance. “It felt very good,” he said. “Even though I lost the first set, I thought I didn’t do too many things wrong. It was a thrilling tiebreaker. He was 6-3 up, two double-faults. I had, I think, only one set point. He just played a good point. I was in the rally but he was going for his shots. In the end he managed to win that very long first set. I was on top of his second serves, putting a lot of pressure. I thought I played very well in the second set especially, but the third as well.”

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