A former jumps jockey who won Australia's most gruelling race has landed the major Flat race as a trainer at the Warrnambool May Carnival.

Shane Jackson won the 2020 Grand Annual Steeplechase (5500m) on Ablaze and was in the winner's circle on Thursday as the trainer of Listed Warrnambool Cup (2350m) winner Mystery Island.

After retiring from race riding, Jackson joined the Warrnambool stable of Lindsey Smith as an assistant trainer and has turned out 32 runners in his name since being granted a trainer's licence in 2022, registering three wins.

All three victories have come with Mystery Island who carries the colours of Americain, the 2010 Melbourne Cup winner.

"It's unbelievable. What a horse," Jackson said.

"I said he deserved to win a good race. I was very nervous with the ground, but Harry gave him a beautiful ride and snuck up on the fence when others were trying to get off.

"None of this would be possible without the Lindsey Smith team and Lindsey handed me this horse to have in my own name.

"The owners Colleen and Kevin Bamford are overseas at the minute and to train a winner for Gerry Ryan in these colours, for people like that, I'm very privileged."

Ridden by Harry Coffey, Mystery Island ($14) raced to a 4-1/2 length win from No Apology ($26) with the $4.60 favourite Little Mix a long neck away third.

Jackson said he held concerns about the 'gluey' ground on Thursday, but Coffey was able to plot a path near the inside while keeping the gelding comfortable in his action.

"I've been riding the horse all prep in some really strong races and he's been flying," Coffey said.

"Every time I get on him, the horse fills you with confidence, he felt great going to the start and he looks amazing.

"I just thought if I can get this bloke to travel and be confident for as long as he can, we might have something left at the end.

"That he did. He knew he was on his home track, and he let rip at the end."

The Lindsey Smith team earlier in carnival took out the feature sprint with Tuvalu landing the Listed Wangoom Handicap (1200m) on day two.