Apprentice Beau Mertens has vowed to make Craig Williams work hard for a sixth Melbourne jockeys' premiership at the season's final meeting.

Williams extended his lead to four in the title race after claiming a winning double early on Wednesday's Sandown program before Mertens hit back with a winner later in the day.

Mertens won aboard Diamond Grace for his master Mick Kent in the Spicer Thoroughbreds Handicap to be three behind Williams ahead of the final meeting at Caulfield on Saturday.

The victory broke a run of outs in the city area for the apprentice.

"It's good to get a winner," Mertens said.

"I'd gone a couple of meetings without a winner which was a bit tough and I'm certainly happy to get one on the board.

"Even though Craig had that early double, you can't give up on them.

"There's still Saturday to go and I'm not giving up yet."

Williams said it was a lovely place to be in going into the final city meeting of the season, although he would have preferred to be a little further in front having just missed a treble when Sacred Theme was narrowly beaten in the Le Pine Funerals Handicap.

"I'm looking forward to the last day," Williams said.

"I've had a look at my rides, I haven't looked at his, and I've got some good rides.

"We've got a bit of work to do because it's not over until the completion on Saturday, but it's made a great race of it."

Williams has a full book of nine rides on Saturday while Mertens has eight, including favourite Supido in the day's feature, the Group Three Bletchingly Stakes.