Three years ago he started favourite in the Melbourne Cup and 12 months later he was fighting for his life.

Now, at the age of eight, he's the form horse of the Melbourne spring with a Group One win against his name.

Alcopop, a horse who has fought his way through form slumps, disease and injury, claimed his first win at racing's top level in the Mackinnon Stakes (2000m) at Flemington on Saturday.

For trainer Jake Stephens it was the success that justified the time and faith he's put into his horse.

But it also proved a bitter-sweet experience.

Stephens took the difficult decision to replace regular jockey Dominic Tourneur with Craig Williams in the Mackinnon.

"As a trainer you've got to be ruthless at times," Stephens said.

"I just hope Dom gets some satisfaction out of the win."

Tourneur had ridden the horse in 20 of his previous 32 starts, including his past two in which he was second in the Caulfield Stakes behind Cox Plate winner Alcopop and runner up to Dunaden in the Caulfield Cup.

"I had to distance myself from it emotionally, but it hurt," he said.

Alcopop raced himself into favouritism for the 2009 Melbourne Cup and finished a fine sixth to Shocking, only to be struck down by a serious lung infection.

He came back into training for the 2010 Cup but suffered a knee injury which Stephens said had been a blessing in disguise.

"The year off and having the knee injury has helped his lungs to recover," he said.

"This has been the preparation where everything has gone smoothly."

Alcopop ($6) finished more strongly than any horse in the race to beat Glass Harmonium ($14).

The $1.70 favourite Ocean Park ran on moderately for third a further long neck back.

With this year's Cup out of the question for Alcopop, Stephens will send him away for a long break with a view to returning next spring for another shot at the big one.