ATP World Tour Finals: Djokovic mauls Cilic in opener

Novak Djokovic began his challenge for a hat-trick of ATP World Tour Finals triumphs in London with a 6-1, 6-1 demolition of Croatia's Marin Cilic.

The Serbian world number one produced a ruthless display against a ragged U.S. Open champion, opening his Group A account with a 56-minute masterclass.

The 27-year-old has now won 28 consecutive matches indoors dating back to 2012 and should he win his remaining two group matches against Stanislas Wawrinka and Tomas Berdych he will be guaranteed to end the year on top of the rankings.

Cilic won the opening five points of the match but his debut at the ATP's prestige event quickly turned sour as Djokovic turned up the heat with a clinical display.

The only blemish was dropping his serve early in the second set but even then he broke again immediately to snuff out any chance of a Cilic fightback.

You have to go back to the Paris Masters in 2012 for the Serb's last defeat under a roof when he lost to American Sam Querrey. Since then he has been untouchable.

"I like outdoor hard courts, as well. I love playing on clay and grass not too bad," smiled this year's Wimbledon champion.

"But indoor has been very successful the last couple years.

"I don't play too many indoor events. As a matter of fact, only two, Paris and London. But I give myself a lot of time to prepare for these events. I enjoy them. I really do."

That was beyond question, but for Cilic his first taste of ATP World Tour Finals action was not much fun.

Although the 26-year-old was not too downhearted.

"You know, there are two more matches. Luckily this is the first one where I played bad," he said.

"There is still the opportunity to go through. That's a positive part of it."

Image: Novak Djokovic of Serbia in action against Marin Cilic of Croatia in their round robin match during the ATP World Tour Finals at the O2 Arena in London.

Photo: Justin Setterfield/Getty Images