Jamie Spencer is now favourite to win the champion jockey's crown after titleholder Frankie Dettori broke a collarbone in a fall at Sandown Park on Saturday.
Spencer, 25, rode five winners at two meetings on Saturday and, at 36 clear of Dettori with less than half the season remaining, has an outstanding chance of lifting the championship for the first time.
Bookmakers rate the Irishman as 5-6 favourite. Dettori, who could be out of action for up to six weeks, has been pushed out to 8-1 from 7-4.
It was an unhappy weekend for the Italian. French Derby winner Shamardal, his mount in Saturday's Group One Eclipse Stakes, had to be pulled out the day before after suffering a career-ending fetlock injury.
Dettori has had a mixed season, enjoying two French classic triumphs on Shamardal but failing in the Epsom Derby again and missing out on the Royal Ascot meeting while serving a six-day ban for careless riding.