Trainer Robbie Laing had weight of numbers on his side but it was a runner from the David Brideoake stable who broke his maiden in the opening race at Sandown.
Laing saddled up three of the five runners in Wednesday's Thebigscreencompany Plate (1400m) but had to settle for second, third and fifth as Dalgety handled the heavy conditions to win for the first time at his third start.
The opening two races at the meeting were transferred to the Hillside course because of surface water on the Lakeside track at the 1300m following heavy rain.
Horses in the first two races did not have to race on the affected part given the Hillside's bigger circumference.
Dalgety, ridden by Daniel Moor, drew away late to win by 3-1/4 lengths over the Laing-trained Superior Rose with her stablemate Penthouse Poet another nose away.
"Daniel thought he would be better with the sting out of the ground," Brideoake's stable representative Alex Woodhams said.
"You don't know if any horse is going to get through it this heavy, but he looked like he handled it beautifully.
"I think we'll only see the best of him the older he gets and further he gets."