Boss is the most successful jockey in the history of this Group 1 race which dates back 156 years. The famous mile handicap is one of seven races - including four Group 1s - which are scheduled on the card.
Kerry Parker-trained five-year-old Think It Over, arguably the most improved horse in Australia this year, highlighted his credentials for Saturday's race with an excellent win in the G1 George Ryder Stakes (1500m) at Rosehill Racecourse on 27 March.
Eleven of the past 20 Doncaster Mile winners have come through the George Ryder Stakes with all bar one having finished in the first three in the lead-up race.
Think It Over is drawn barrier 18 (but will start from 16 if the two reserve runners do not gain a start) but wide draws are rarely an issue in major mile handicap contests at Randwick and certainly not for the jockey - as five of Boss' seven Doncaster Mile winners have drawn double figure gates.
The 51-year-old Boss has made the most of limited opportunities since his return from Singapore two years ago with four Group 1 wins this season and last in Australia, plus victories in the lucrative The Everest and Golden Eagle (which do not have G1 status).
"If you give me a chance in a good race, that's the result," he said after winning last Saturday's G1 Tancred Stakes (2400m) - his 90th win at the top level which is tally bettered only by Damien Oliver and Hugh Bowman among current riders.
Parker credits Boss with playing a key part in the improvement of Think It Over, who hadn't won beyond G3 level before this year.
"We knew this bloke had the talent but Glen has made him into a racehorse. His feedback is unbelievable and makes my job easier. He has confidence in the horse and his rides have been perfect," Parker said this week.
Kris Lees-trained and Hugh Bowman-ridden, last start AU$5 million All Star Mile winner Mugatoo is favourite for the race from Think it Over, three-year-old Mo'unga and the Gai Waterhouse and Adrian Bott-trained Yao Dash.
Waterhouse has trained seven Doncaster Mile winners - a record tally she shares with her late father Tommy Smith.
The Randwick track, which is right-handed (circumference 2224m, straight 410m), was rated soft on Wednesday (7 April) afternoon and further showers are forecast in Sydney this week.