Jockey Beau Mertens never knows which Cismontane he'll be riding each time he gets in the saddle.

Mertens has galloped Cismontane on the training track at Flemington a number of times while he pairs up with the gelding for the third time on race day in Saturday's Mornington Cup.

The Gai Waterhouse and Adrian Bott-trained stayer gave Mertens his first Melbourne Cup experience when he finished 13th behind Rekindling in last year's race.

The only other time Mertens has ridden the stayer was when he ran second in a 2400m-handicap at Sandown last July.

With regular jockey Stephen Baster riding at the Golden Slipper meeting in Sydney, Mertens got the call-up.

"He's a bit off and on and you never quite know what you're going to get," Mertens said.

"He's either dead quiet or pulling really hard.

"He can be a difficult horse to ride but once he gets relaxed and in his rhythm he can be a really good stayer."

Following a first-up fifth to Homesman in the Mornington Cup Prelude at Caulfield on February 24, Cismontane had a trip to Warrnambool for a hurdle school.

"Usually schooling switches them on and getting them wanting to do things and I think he's benefited from that," Mertens said.

Cismontaine showed his staying qualities last spring, finishing third in the Moonee Valley Cup before winning the Lexus Stakes a week later at Flemington to earn a berth in the Melbourne Cup.

Mertens cites Cismontane's win at Moonee Valley early in the season as an encouraging sign he will handle Mornington.

"It's a tight, turning track and it does favour on-pace runners most of the time," he said.

"If everything goes our way he should be in the finish."

With Lord Fandango scratched and Sydney bound for Saturday's Manion Cup at Rosehill, and Foundry also missing, Cismontane sits on the fourth line of betting at $9.50.

Kings Will Dream, aiming to maintain his perfect Australian record, dominates betting at $2.30 with his Darren Weir-trained stablemates Bondeiger ($6) and Gallic Chieftain ($8) next in market order.