Partnering the Joseph O’Brien-trained runner, Dettori passed the post in second place behind Vow And Declare after a tight four-way finish to the two-mile prize, with Prince Of Arran third and Il Paradiso fourth.
However, Dettori’s mount drifted across the track in the final half-furlong, impeding the run of Il Paradiso, who was trying to challenge between Master Of Reality and Vow And Declare.
Wayne Lordan had to stop riding aboard Il Paradiso, who is trained by O’Brien’s father, Aidan, and the stewards quickly called an inquiry before eventually opting to demote Master Of Reality to fourth and suspend Dettori until November 14.
The Charlie Fellowes-trained Prince Of Arran was promoted to second – one place better than last year – with Il Paradiso boosted to third.
Joseph O’Brien won the 2017 Melbourne Cup with Rekindling and he was disappointed Master Of Reality could not give Dettori his first win in the race, with the Italian having twice finished second in 1999 and 2015.
He said: “I’m more gutted for Frankie than I am for myself. I’ll be back. I don’t know if Frankie is ever going to win this race.”
Dettori has enjoyed a stellar year with 19 Group One winners, including three for super-mare Enable and another Stayers’ Million prize with Stradivarius.
He has endured a luckless run at Flemington, with his 17th ride on Master Of Reality resulting in a suspension that began immediately after pleading guilty to a charge of careless riding.
Dettori was suspended for a month and fined $20,000 for causing interference on runner-up Max Dynamite four years ago and suspended for a month for careless riding on Mamool in 2004.