Apprentice Beau Mertens has kept his nose in front in the Melbourne jockeys' premiership after maintaining a perfect record aboard the Ciaron Maher-trained Schism.

Mertens has only be aboard Schism in four of her 16 starts but remains unbeaten on the mare after guiding her to an all-the-way win in Saturday's OTI Racing Handicap (1400m) at Caulfield in the final race of the day.

It put Mertens back in front by one win in the Melbourne premiership with four meetings remaining after rival Craig Williams had drawn level with a winning double earlier the program aboard Orient Line and Moonlites Choice.

"It was a bit of a long day but I knew she would be able to get me out of the hole, and she did," Mertens said.

"I was hoping to end the day out in front and it has happened. If I can just keep doing what I'm doing and keep getting these winners and keep my nose in front, hopefully things can work out."

Schism brought up her third-straight city win with a determined display, backing up a week after taking out the Leilani Series Final at Flemington last Saturday.

Sent out the $2.50 favourite, Schism went to the front and held off the challenge of Onerous in the straight to win by a long neck, with Airalign another 2-3/4 lengths back in third.

Maher said Schism would be given a freshen-up before targeting a stakes win in mares' grade early in the spring.