Constitution Hill won under the floodlights at Kempton Park to make it two wins from two on the Flat after moving from National Hunt racing.
Having won his first 10 races over the fences, including the 2023 Champion Hurdle at Cheltenham, the Nicky Henderson-trained horse switched to the Flat after three falls in the four races.
Following a debut victory in the Road to Cheltenham Novice Stakes at Southwell last month, the nine-year-old roared to success again after starting out as the 1-7 favourite.
In fifth place for much of the race, jockey Ryan Moore took him to the front to finish clear of Classical Allusion, with Keep It Cool third.
Moore said: “He’s a gentleman and I think the horse is enjoying his runs on the Flat. He moves really well and I think there will be plenty more improvement to come. He went to the line with his ears pricked.
“We don’t know what his level is yet, he will tell us. We will know more on his next one. I think he’s very comfortable at 12 [furlongs].”
“He’s not slow, on a sharp track like this he seems to handle it well,” added Henderson. “It’s a different sport to be honest with you, compared to two miles at Cheltenham.”