Grand stayer Who Shot Thebarman has finally had his day in the sun with a last-stride win in the $2 million Sydney Cup at his fifth attempt.

Who Shot Thebarman finished strongly on the outside to beat Zacada by a nose in the time-honoured 3200m handicap at Randwick.

The nine-year-old's win gave premier Sydney trainer Chris Waller a third Group One win in successive races on Saturday.

Who Shot Thebarman had twice finished second in the Sydney Cup, including last year in the rescheduled race.

The first running of the 2017 Sydney Cup was declared a no-race when two horses fell, including Who Shot Thebarman, amid safety concerns with the stricken Almoonqith still on the track.

Along with his Sydney Cup placings, the former New Zealand stayer, and 2014 Auckland Cup winner, has also finished third in one of his three Melbourne Cup appearances and fifth in another.

"He's been such a frustrating horse because he's run so many great seconds and thirds in Sydney Cups and Melbourne Cups," Waller said.

"He's given us one hell of a ride.

"He's nine years old and if Winx is not a pretty good advertisement on how to look after a horse I think Thebarman takes the cake.

"That's the best he's looked today as a nine-year-old. He was a test as a younger horse and we haven't given up on him and looked after him."

There was drama pre-race when Japanese visitor Pre Stwick was scratched on veterinary advice behind the barriers.

The vet checks were prompted after jockey Joao Moreira was not happy with the horse's action.

Who Shot Thebarman ($18), with Blake Shinn aboard, settled back before working into the race around the field approaching the home turn.

Dean Holland saved ground on New Zealand stayer Zacada ($91) and raced through on the fence to hit the front at the 200m but Who Shot Thebarman got the bob of the head on the line.

Sir Charles Road ($7) was another length away third.

Shinn said if ever a horse deserved a Sydney Cup, it was Who Shot Thebarman.

"I'm just rapt for the horse, and the owners," Shinn said.

"The horse deserves the recognition, to win a real big Group One."