Alexander Zverev upset Novak Djokovic to claim the biggest title of his career with a 6-4, 6-3 victory at the ATP Finals on Sunday.

The 21-year-old Zverev is the youngest champion of the season-ending event since Djokovic claimed the first of his five titles a decade ago, and the first from Germany since 1995.

Top-ranked Djokovic was attempting to tie Roger Federer’s record of six titles but followed the same path as the Swiss great, who lost to Zverev in the semifinals at the O2 Arena.

Djokovic’s serve hadn’t been broken all tournament until the final. Zverev did it once in the first set and three times in the second, completing the victory with a spectacular backhand winner up the line.

Earlier, American pair Mike Bryan and Jack Sock saved a match point in the deciding tiebreaker to beat Pierre-Hughes Herbert and Nicolas Mahut 5-7, 6-1, 13-11 for their first ATP Finals doubles title together.

Having failed to take advantage of five championship points during the first-to-10 match tiebreaker, Bryan and Sock then had to save one against their French opponents before finally closing out victory.

“It was a hell of a match,” Bryan said.

The 40-year-old Bryan has now won the tournament five times. He won four times with his usual partner _ and brother _ Bob, who has been out with an injured hip since May.

Sock and Bryan have dominated since teaming up, winning Wimbledon and the U.S. Open before finishing their season in style in London.

“It’s been a hell of a ride,” Bryan said. “This could be our last hoorah because Bob’s training back in Florida.”

After reaching the singles semifinals last year, Sock has endured a torrid season in that format, falling outside the top-100 ranked players. However, he became the first American since John McEnroe to add a doubles final appearance at the tournament to his last-four singles showing.

“This is special because it was a pretty bad year in singles,” Sock said. “This makes up for some of the low moments I’ve had.”

The French duo’s season is not over yet. Herbert and Mahut are part of their nation’s squad for the Davis Cup final against Croatia, which starts in Lille on Friday.

Courtesy: Associated Press