Geelong skipper Tom Harley has attempted to claim underdog status in Sunday's blockbuster against St Kilda at Etihad Stadium in the clash of the AFL's two unbeaten teams.

It is the first time ever two unbeaten teams have met this late in the season with both teams having recorded 13 successive wins to start 2009, although the Saints are in top position courtesy of their vastly superior percentage.

While the Cats' percentage of 149.7 is still some 25 percent in front of the next best team - the third-placed Western Bulldogs - it is dwarfed by the Saints' percentage of 177.5.

And that is mostly due to the fact that the Saints are on course to produce the greatest defensive performance by any team since the competition reverted to 22 rounds in 1970 - having conceded just 764 points in 13 rounds at an average of just under 59 points per game.

The Cats have conceded over 200 points more for the season at 1008 but have outscored the Saints so far in booting 1509 to 1356 points.

But Harley insisted on Tuesday that the Saints deserved favouritism despite the fact the Cats have won 55 of their past 58 matches - the most sustained run of success by any team in history - while the Saints have merely won 13 in a row after being thrashed by both Geelong and eventual premiers Hawthorn during last year's finals series.

"I think if you are talking favourites then they probably deserve it just by virtue of the fact they have got the numbers to back them up," Harley told Channel Ten on Tuesday.

But the bookmakers disagree with Victoria's TAB Sportsbet listing the Cats as clear $1.55 favourites while the Saints are listed at $2.35.

While the Saints are coming off an emphatic win over Richmond - which failed to score for two quarters during last Sunday's clash at Etihad Stadium - the Cats have been less than impressive in their past three wins against West Coast, Fremantle and Port Adelaide, which outscored the Cats in two quarters last Sunday at Skilled Stadium.

However while Harley was quick to anoint the Saints as favourites, he was equally quick to defend the form of his team.

"Our form is pretty good," Harley said.

"To say we are patchy and a bit out of touch is as much as anything doing a bit of disservice to the rest of the competition because we are beating then so what does that say about those sides."

The Cats went through a light training session on Tuesday with Gary Ablett missing the session although the Brownlow Medal favourite is expected to play on Sunday.

In-form goalsneak Shannon Byrnes, who has kicked nine goals in the past two weeks, is battling a bruised hand but is also expected to line-up but the Cats will have to replace injured defender David Johnson with David Wojcinski expected to get the nod.