Dubuisson had eight birdies and two bogeys along with the fourth-hole double bogey 6 Thursday for a 4-under-par 68 and a two-stroke lead after the first round.
Tricky wind conditions at the Blackstone Golf Club made play tough Thursday and only 17 golfers in the field of 156 broke par.
Casey, Foster and Donaldson each had four birdies and two bogeys while Jung carded three birdies and one bogey. Ramsay's round included five birdies, a bogey and a 7 at the par-5 fifth hole.
Dubuisson opened play Thursday at No. 10 with a bogey but was 2-under for the day after six holes. He had another bogey at the 16th hole before closing his first nine with back-to-back birdies.
He made it three in a row at the first hole. A poor drive led to a penalty shot and the double-bogey 6 at the fourth hole. He moved out front with birdies at Nos. 5 and 6.