Charlie Appleby's colt claimed his fourth win from five career starts in the Gordon Stakes at Goodwood on his latest appearance, readily accounting for subsequent Great Voltigeur winner Deauville Legend.
Thirteen horses could go to post for the season's final Classic on September 10, although there's still a chance of further additions to the Leger field, with trainers having the option to supplement horses at a cost of £50,000 on September 5.
Appleby, who won last year's St Leger with Hurricane Lane, could also saddle Secret State, who finished second to Deauville Legend when bidding for a fifth successive victory at York last week.
Six-time Leger-winning trainer Aidan O'Brien, meanwhile, has five remaining contenders, with Anchorage, Bluegrass, United Nations, Waterville and Emily Dickinson all in the mix.
Roger Varian - successful in 2014 with Kingston Hill - is set to be represented by Eldar Eldarov, who has been given a break since losing his unbeaten record in the Grand Prix de Paris in July, while Zechariah looks a likely runner for Freddie and Martyn Meade following his recent success in the Geoffrey Freer Stakes at Newbury.
The potential field is completed by Paddy Twomey's French Claim, Derby runner-up and Gordon Stakes third Hoo Ya Mal, who is now in the care of George Boughey, Ivan Furtado's filly Lizzie Jean and the Marco Botti-trained Giavellotto, who bolted up in a Newmarket handicap on his latest appearance.
Botti said: "We know it's a big jump from a handicap to the St Leger, but that is the plan.
"He's a horse who has done nothing wrong and has kept improving. It has just taken a while for the penny to drop, but he was impressive at Newmarket and stays well.
"As long as the horse is fine we'll take our chance. Obviously it's a Classic and you expect it's going to be a really tough race, but I think he probably deserves to take his chance and we'll see how he goes.""