Roger Federer got his quest for a fifth Masters Cup title off to the worst possible start with a 3-set loss to Frenchman Gilles Simon.
The Swiss top seed, who withdrew from the Paris Masters 11 days ago with a back injury, made 50 unforced errors to fall to a second defeat in two encounters with the 23-year-old world number nine.
Federer says the better you play, the better he plays, he's quite an unusual player and he makes you work hard and runs very well.
The world number two also lost to Simon at the Toronto Masters in July.
Federer says he definitely missed shots I normally doesn't miss and he thinks that's just lack of practice.
Third seed Andy Murray blew hot and cold on his Masters Cup debut, before beating Andy Roddick in 3 sets in the other match in the Red Group, from which two players will qualify for Saturday's semi-finals.
Federer lost his only previous Masters Cup group match to Chile's Fernando Gonzalez in his opening encounter last year but still managed to claim the title for the second season in a row.