Alexander Zverev stunned world No. 1 Novak Djokovic in straight sets to win the season-ending ATP Finals and earn the biggest victory of his career.

Djokovic, 31, was the heavy favourite to win a sixth finals title but was outclassed 6-4 6-3 by the German.

Third seed Zverev broke Djokovic for a 5-4 lead in the first set and then served three big aces to take the set.

Zverev, 21, continued to dominate in the second set and sealed a memorable victory as Djokovic faltered.

“I’m unbelievably happy, obviously it is the biggest title I have ever won,” said Zverev, who also took home around £2m in prize money.

Zverev lost to the Serb in straight sets in the round-robin stage but, after beating Roger Federer in Saturday’s semi-finals, produced a more confident performance to stop Djokovic equalling Federer’s haul of end-of-season titles.

Zverev missed his first championship point before hitting a sensational backhand down the line for victory, falling to the court in a mixture of disbelief and celebration as Djokovic jumped over the net to congratulate him.