( 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 . 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 . 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 did n'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 .
Novak Djokovic wins opening match in Marin Cilic . Beats U.S. Open champion Marin Cilic three -1 6-1 . Stanislas Wawrinka thrashes Tomas Berdcyh by same margin . 11th day wins for Roger Federer and Roger Federer .