Punters have opened their pockets early to plunge on the Mark Kavanagh-trained Instalment returning a winner at Flemington on Saturday.

In what TAB Sportsbet described as one of the biggest pre-post "goes" in a long time, Instalment has been hammered from $7.50 into $3.10.

"Punters wasted no time in hooking into this one," TAB Sportsbet's Glenn Munsie said.

"A handful of customers were relentless in backing him at every turn in.

"They were not overly large bets but by the time they finished, over $22,000 had been invested in a two hour period to win just over $70,000.

"This sort of activity early is rare but they evidently had a plan just to get on and keep betting until their bank ran out."

Instalment has raced six times for three wins including a victory over Sharnee Rose in the Listed MSS Security Stakes (1100m) at Flemington at his most recent appearance in March.

He will resume against a handy field in Saturday's Bob Skilton Handicap (1100m) which includes African Pulse who is undefeated in three first-up runs.

The Mike Moroney-trained African Pulse has retained favouritism at $2.90 despite the plunge on Instalment who is now the clear second pick.

Baron Douro, who has won his past two starts at the track, is $8.50 with Bombalatomba, Our Lucky Rain and Shanghai Warrior all $9.