Kevin Ryan's inmate had a whale of the time on the Knavesmire and was too quick Spring Loaded, who finished a length and three-quarters away in the valuable five-furlong dash.
Flying Pursuit and Eastern Impact were third and fourth respectively.
Ryan said: "I thought Teruntum Star had a great chance in the Ayr Gold Cup (which was abandoned) and wasn't worried about the 7lb rise in the weights.
"We'll run him again before the end of the season, maybe try to find a race in France, then aim him at the big six-furlong handicaps next year."
Rebel Assault showed plenty of grit to cause a 25-1 upset in the coral.co.uk Rockingham Stakes.
Mark Johnston's juvenile was always prominent under Franny Norton and did particularly well to fend off It Dont Come Easy by a length and a quarter.
Staxton finished third, with even-money favourite Shabaaby rather one-paced in fourth.
Deirdre Johnston, wife of the winning trainer, said: "She lost her race at the start in France last time so we thought it was worth having another go here for the black type.
"We've thought a lot of her all season. She's as tough as old boots."