Punters have determined the Lightning Stakes is a two-horse race between Lankan Rupee and Deep Field.

But in a complete swing around from first markets, the lightly raced Deep Field is now the clear-cut favourite.

Deep Field has firmed from $2.50 to $2.20 while Horse of the Year Lankan Rupee has eased from $2.20 to $2.50 with the TAB.

John Hawkes, who trains the unbeaten Deep Field in partnership with sons Michael and Wayne, admits it is a big task for the four-year-old who has been to the races just five times.

"It's a big test taking on a four-time Group One winner but he's earned his spot and you've got to have a go," Hawkes said.

"There's only six runners and there's always going to tactics.

"It's a competitive race and you've just got to do your best."

Three-year-old Group One winner Brazen Beau is the only other runner under double figures in the six-horse Lightning (1000m) at $5.

Trent Langskaill, media spokesman for TAB, said Deep Field and Lankan Rupee had accounted for 95 per cent of total bets taken on Saturday's race.

"It's about 60 per cent in favour of Deep Field over Lankan Rupee," Langskaill said.

"There is no question they dominate the betting. There has been a little bit for Brazen Beau but not much for the other three."

Langskaill said bookmakers orignally posted Lankan Rupee favourite based on his experience but punters took the odds on Deep Field's untapped potential.

Deep Field will be having his first test in Group One company while Lankan Rupee's four elite wins include last year's Newmarket Handicap over the straight 1200-metre course.

Hawkes said he was not looking any further afield than Saturday, noting that Deep Field was taking on experienced horses and that he is still learning.

"I'm just worrying about Saturday," he said.

"We don't want to get too far ahead of ourselves and as long as he runs well, we'll take stock from there."

LIGHTNING STAKES FAVOURITES

LANKAN RUPEE

* Five-year-old gelding who has won 10 of 20 starts and earned more than $3.6 million prize money

* Winner of four Group One races (2014 Oakleigh Plate, Newmarket Handicap, TJ Smith Stakes, Manikato Stakes)

* 2013/14 Australian Racehorse of the Year and the equal highest-rated sprinter in the world

DEEP FIELD

* Four-year-old entire unbeaten in five starts with a combined winning margin of 24 lengths

* Facing his first Group One test

* Won Group Two sprint on the straight course at Flemington last spring

* Track record holder over 1100m at Canterbury