Eagles on the par-5 fourth and par-4 13th holes negated three bogeys at the famed Wentworth Golf Club in Virginia Water, England.
"I always used to watch this event as a kid and dreamt of being here and here I am," Casey told the BBC. "It's very cool."
His 36-hole total, 8-under 136, leads countrymen Anthony Wall (71) and David Horsey (71), Spain's Miguel Angel Jimenez (70), the defending champion, Scotland's Marc Warren (66) and Denmark's Soren Kjeldsen (69).
Jimenez hopes to become just the third player ever to defend his title with Nick Faldo and Colin Montgomerie.
South Africa's Thomas Aiken (67), American Ben Curtis (70) and Stephen Dodd (68) of Wales share seventh place at 7-under 139.
Among those missing the cut were Argentina's Angel Cabrera (149), Sweden's Mikael Lundberg (151) and England's Lee Westwood (154).
Copyright 2009 by United Press International.