Roger Federer goes into his Masters Cup opener against Fernando Gonzalez with a 10-0 head-to-head record

Gonzalez looks set to suffer again at the hands of Federer after dropping the first set 6-3

But the Chilean forces the second set into a tiebreak and shocks the world number one by taking it 7-1

Federer, who has never lost a Masters Cup round-robin match, loses his cool and even argues with the umpire

And Federer's mood is not helped when his opponent saves five break points in the deciding set

Gonzalez's brutal forehand does most of the damage and two rasping winners help him to the crucial break at 5-5

Gonzalez holds his nerve to serve out victory as Federer loses consecutive matches for the first time since 2003

In Monday's other Red Group match, Andy Roddick defeats Nikolay Davydenko 6-3 4-6 6-2

There is a brief delay as Davydenko challenges a call on match point - but there is no reprieve for the Russian