Overturn led from start to finish to lift the Chester Cup for Grand National-winning trainer Donald McCain.
The 11-2 shot burst out of stall one under Eddie Ahern and only Tastahil was able to keep him in his sights.
Tastahil finished second, with Mystery Star third and Mount Athos fourth.
Earlier, hot favourite Wonder of Wonders (6-5), trained by Aidan O'Brien and ridden by Ryan Moore, won the Cheshire Oaks, beating Blaise Chorus by two and three quarter lengths.
But the day's feature race went to a horse trained locally by McCain, son of the legendary trainer Ginger McCain.
Solid in the betting, Overturn had been expected to start favourite until a late gamble on Red Cadeaux pushed his price out to 11-2.
But he quickly found himself well clear of much of the field, and was able to sustain his advantage despite the two-mile trip.
Having sent Ballabriggs to glory in April's Grand National, McCain had been bullish about the seven-year-old's chances.
Overturn had finished seventh in the Champion Hurdle but relished his first appearance on the Flat since last August - and Ahern was more than happy to let him lead the field as he made the most of his draw tight to the rail.
His final margin of victory was a length and three quarters.
McCain said: "He's a fantastic little horse. He's an absolute joy and on his day he's a hell of a horse to pass.
"It's great to come here. As a boy I grew up watching the likes of Sea Pigeon win this and dreamed of having a winner here."
Ahern added: "He gives himself a breather, he fills his lungs with air and takes off. He could nearly have gone round again."
Meanwhile, Wonder Of Wonders' part-owner Michael Tabor gave his filly his approval for Epsom after her encouraging victory in the preceding race.
It was the third time O'Brien had landed this Listed event in the last four years, and his latest winner showed a nice turn of foot to catch up the runaway Blaise Chorus.
"Ryan was very happy with her, as you well should be," said Tabor.
"Why wouldn't you go for the Oaks now? That will be the next run for her unless Aidan has other ideas, and I doubt that."
She is a best-priced 10-1 to win the Oaks.