Novak Djokovic was celebrating victory in less than an hour against Marin Cilic at the ATP World Tour Finals.

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Novak Djokovic wins opening match in ATP World Tour Finals

Beats U.S. Open champion Marin Cilic 6-1 6-1

Stanislas Wawrinka thrashes Tomas Berdcyh by same margin

First day wins for Roger Federer and Kei Nishikori

CNN  — 

Novak Djokovic was a man in a hurry.

The two-time defending champion at the ATP World Tour Finals might have been expected to be tested by the new U.S. Open champion Marin Cilic, in their Group A opener, but it turned in to a one-sided rout Monday.

World number one Djokovic broke the giant Croatian no less than six times on his way to a 6-1 6-1 victory in less than an hour at the 02 Arena in London.

It was the Serbian’s 11th straight victory at the end of season event and his 28th straight in matches played indoors.

Read: Nishikori makes dream debut

Cilic’s powerful serve, which so helped him to his grand slam triumph at Flushing Meadow, was rendered impotent by the returning brilliance of the number one seed,

“It was a great performance obviously,” he said after his quickfire victory.

“Marin was a U.S. Open winner but I managed to neutralize his service and get a lot of balls back in play.”

Djokovic, who is looking to wrap up the season-ending No.1 ranking, will achieve that feat if he reaches the semifinal stage with a 3-0 winning record from the round-robin group.

He plays Stanislas Wawrinka of Switzerland next on Wednesday and the Australian Open champion was also a commanding winner in his group opener.

Wawrinka also dropped just two games in beating giant Czech Tomas Berdych in a little over an hour.

The number three seed has been in poor recent form, but he showed a big improvement against the misfiring Berdych, who made 24 errors.

Read: Djokovic beats Raonic for Paris crown

He was damning in his verdict of his performance following the defeat.

“Well, unfortunately it was my worst match of the whole season,” Berdych told the ATP World Tour website.

“My game is about hitting the ball nice, clean, then you can create something. But that’s the beginning of what I didn’t have today at all. I hit so many frames.”

Spectators at the prestigious eight-man event have now seen four matches with four straight sets victories, the pattern started as Japan’s Kei Nishikori beat home favorite Andy Murray 6-4 6-4 in the opener Sunday.

Roger Federer, who can still pip Djokovic to the top ranking, followed up with a 6-1 7-6 win over Milos Raonic as he began his quest for a record seventh ATP World Tour Finals crown.

Read: Federer closes on Djokovic with Basel triumph