Alexander Zverev breaks down on court after beating Novak Djokovic at ATP Tour Finals

The young German was emotional after he beat the world No 1 in straight sets 6-4 6-3 to stun the tennis world.

He collapsed to the ground and hid his wet eyes after producing the most important victory of his career.

Djokovic was expected to finish a spectacular season, where he won two Grand Slams, in style this week.

But Zverev won the biggest title of his career so far under the lights in London.

READ MORE: HOW ALEXANDER ZVEREV BEAT NOVAK DJOKOVIC

Zverev pockets $2,509,000 and 1,300 ATP Ranking points to finish the year as world No 4.

"I really can't describe it. It is the biggest title I have ever won,” he said.

"Firstly I want to congratulate Novak and we may never have seen the tennis he has played in the last few months before. He barely lost a match but thankfully he did to me.

Zverev then puts the trophy back on the stand and jokes: "I am going to cramp in a second! I need to put this down"

He continued: "We [Djokovic and Zverev] had so many talks, not only about tennis but all different types of subjects - I won't mention what - but you are a sharing person and you have shared some titles with me. I appreciate you letting me win one today.

"Also huge congratulations to the whole Djokovic team. Finishing as world number one after having surgery this year, I don't know if that has been done before. You are one of the best teams on tour so good luck for next year.”

Djokovic paid tribute to the new champion and said: "Sascha [Zverev] definitely played much better than he did in the group stage.

“He deserved to win, he's still quite young but he's had an amazing career so far and I wish him all the best for his future.

"Speaking of being young, hopefully I'll play many more years and I'll see you guys here in years to come.

"I want to thank my team for a great season. If we put things in perspective, it was an amazing year, a great comeback so thanks for helping me get to where I am.

"Thank you to the fans for supporting tennis for 11 months. It's a long season but you guys making it very enjoyable for all of us."

Zverev was booed on court yesterday during his match over Roger Federer but got a great reception today on his way to victory.

Novak Djokovic vs Alexander Zverev match summary

The 21-year-old broke serve once in the opening set and three times in the second to pull off a shock victory in a packed 02 Arena - denying Serbian Djokovic a record-equalling sixth title at the ATP's blue-riband event.

Djokovic was a firm favourite having looked unbeatable all week, not dropping a set or even a service game, but 24 hours after being booed following a semi-final win over Roger Federer, Zverev had the crowd drooling over an audacious display.

Zverev is the first German to win the title since Boris Becker in Frankfurt in 1995 and the youngest since Djokovic won at the same age in Shanghai in 2008.

Djokovic had beaten Zverev comfortably in the round-robin phase on Wednesday, but he looked edgy.

At 4-4 in the opener a couple of poor Djokovic forehands gave Zverev the chance to serve for the set and he sealed it thanks to three consecutive aces.

An increasingly ragged Djokovic then dropped his opening two service games of the second set, either side of breaking Zverev for the first time.

With victory looming world number five, Zverev showed no sign of nerves and clinched the title when he sent a backhand winner past a stunned Djomovic.

He collapsed onto his back before Djokovic sportingly walked around to the other side to congratulate him.