England have won the toss and decided to field against Sri Lanka in ICC Champions Cricket trophy at Johannesburg today.Meanwhile, Star opener Gautam Gambhir is all set to play in India's opening encounter at the Champions Trophy against arch-rivals Pakistan at Centurion tomorrow. Gambhir's availability for the crucial opening encounter was in doldrums as the left-handed batsman was recovering from a groin injury sustained during the Sri Lanka tour which forced him to miss the tri-nation Cup.India will play Australia in their second match on Monday and West Indies in their final group match on September 30.Smarting from their first match defeat against Pakistan, West Indies face an uphill task of shocking the mighty Australians if they have to keep their hopes alive in the Champions Trophy tomorrow. Australia, on the other hand, are on a high after their 6-1 win in the just-concluded ODI series against England.