The Soultaker looked to be making heavy weather of it 600m from home before the colt rallied strongly for Du Plessis.
"He was 500 to one, but once we straightened up and I got back to nearer the fence and the stick in my left hand he really took off," Du Plessis said.
The Soultaker, who finished runner-up when resuming in the Listed Northland Breeders' Stakes, has now won two of his seven starts after his success last season in the Listed Murdoch Newell Stakes at Avondale.
He drew out in the closing stages at Ellerslie to beat Hello M'Lady, who was placed in the Listed Wanganui Guineas behind the unbeaten Highlad at her previous start, by a length and a quarter.
"I walked the track and the instructions were to stay closer in, there was no reason to come wide," co-trainer Chris Gibbs said.
"Mark rode him beautifully and when he came off the bridle he kept working on him. The horse showed his class today and there's huge upside to him."
- NZ Racing Desk.