Alexander Zverev earned the biggest victory of his career on Sunday when he stunned world Tennis number one, Novak Djokovic in straight sets to win the season-ending ATP Finals in London.

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

Zverev, who was seeded third at the tournament overtook the 31-year-old Djokovic for a 5-4 lead in the first set before serving three big aces to take the set. The 21-year-old continued to dominate in the second and sealed a memorable victory as Djokovic faltered.

“I’m unbelievably happy. Obviously it is the biggest title I have ever won. How I played today, how I won it, for me, it’s just amazing.,” said Zverev, who took home about £2 million in prize money.

The 6ft 6 inches Zverev had earlier lost to Djokovic in straight sets in the round-robin stage but after defeating Roger Federer in Saturday’s semi-finals, he  produced a more confident performance to stop the Serb from 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.

With his booming serve, crunching ground strokes and improved play around the net, Zverev has long been heralded as the young player most likely to carry the mantle for the men’s game once the likes of Djokovic, Federer, Rafael Nadal and Andy Murray retire.