Apprentice Beau Mertens is entrenched in a battle for the Melbourne jockeys' premiership but the top young rider is fast closing in on another milestone.

Mertens needs only four more city wins to outride his claim.

It raises the prospect of the teenager competing with premiership rival Craig Williams in the final weeks of the season without a claim as the pair battle it out for the coveted title of Melbourne's premier rider.

Mertens currently claims 1.5kg in the city and a winning double on Saturday at Flemington took his season tally in the metropolitan area to 66.

He maintains a one-win lead over five-time premiership winner Williams who also rode a Flemington double, with 10 city meetings remaining.

Being close to notching his 80th city win and outriding his claim is a significant feat for the 19-year-old given he only rode his first metropolitan winner 14 months ago.

Just as it has in the past couple of seasons, this season's Melbourne premiership could go down the wire.

Two seasons ago three riders were all in contention in the final weeks, with Damien Oliver taking the title over Williams and Dwayne Dunn but only three wins separated the trio.

Last season Williams and Dunn fought out the premiership with Williams securing the title at the final meeting of the season, eventually finishing with a four-win advantage.

The premiership battle continues at Sandown on Wednesday with Mertens booked for seven rides on the eight race card.

Williams has a full book of Sandown rides and is relishing the competition.

"It's good for racing," Williams said.

"Beau is riding great. He's making me raise the bar again and it's really good competition.

"He's a great young rider."