Glen Boss knows better than most what it takes to win the $3 million Doncaster Mile.

The champion jockey has won Sydney's showpiece handicap a record five times and is convinced he has secured the ride on a horse with the right profile to add to that haul at Randwick on Saturday.

"It's been a good race to me over the years. I've won five times and been dead-set unlucky twice," Boss said.

"I should have nearly won seven of them."

After winning on Sprint By in 1996 and Private Steer in 2004, Boss's three most recent wins have been on three-year-olds in consecutive years from 2006 to 2008.

And it's a three-year-old Boss has again pinned his hopes on having chased the ride on New Zealand colt El Roca after his close second two starts ago in the Randwick Guineas.

"That (Randwick Guineas run) was the one that said to me `well you can win a Doncaster'," Boss said.

"And he's done nothing up to date to change my mind that he could win it or he can't."

Triple Honour was beaten in a photo finish to the Randwick Guineas two starts before he won the Doncaster with Boss aboard in 2008.

Racing To Win (2006) and Haradasun (2007) both won the George Ryder Stakes before their Doncaster wins, and El Roca was a game third in this year's renewal of the weight-for-age race last start.

"El Roca fits the profile of a lot of those horses that have run well and have won it," Boss said.

"Being a three-year-old that has been running really well at a good level, at weight-for-age, and now he drops back to the handicaps with a light weight."

Messene and Weary are the market leaders and while Boss respects that pair, he rates El Roca's form line as stronger and pinpointed Hawkspur as the horse he fears most.

Hawkspur was fourth in the Ranvet Stakes last start, won by Silent Achiever, and has been freshened for the Doncaster.

"He is coming off a run behind the best horses in Australia. He's coming out of a better form line than any of them," Boss said.

"For mine he's the horse to beat, and I thought El Roca can be right there."