London, Nov 19 (IANS): Alexander Zverev defeated World No. 1 Novak Djokovic 6-4, 6-3 here to win the ATP Finals championship and claim the most important title of his budding career.

The 21-year-old German is the youngest player in nine years to reach the final of tennis elite season-ending event, reports Efe news.

With the Sunday victory over Serbia's Djokovic, who has 14 Grand-Slam titles to his credit, Zverev will climb to fourth in the year-end rankings. The rising star got to the final by defeating Swiss great Roger Federer 7-5, 7-6 (7-5) on Saturday, reports Efe news.

"I really cannot describe it. It's the biggest title I have ever won," Sascha, as he is known, said during the trophy presentation at London's O2 Arena.

Turning to Djokovic, he said: "I want to congratulate you for the second half of this year. You barely lost a match all year though you lost to me. I want to mention how good a person you are."

"You deserved to win and well done," Djokovic told Zverev. "You are still quite young and you have had an amazing career."