Ladbrokes St Leger entries dominated the Absolute Aesthetics March Stakes as Forever Now (4-1) scraped home ahead of 15-8 favourite Alex My Boy.
The John Gosden-trained winner had finished third in the Bahrain Trophy and made nearly all the running in this Listed event.
Johnston's Alex My Boy had little luck, with Joe Fanning finally trying to squeeze up the rail and finishing a short head behind, while Kings Fate plugged on for third.
Winning jockey William Buick said: "He's tough, isn't he? He stayed well, and although he's still immature, he handled the track."
Johnston said of the runner-up: "He was slowly away, again, and on top of that Joe was annoyed with himself for going up the rail.
"He didn't get a clear run and he'd probably be better with ease in the ground. I'd say he'll almost certainly go to Doncaster along with Hartnell."
Sky Bet cut the winner to 16/1 for 25s for the final Classic of the season at Doncaster with Alex My Boy the same price from 20/1,