Australia's No.1 ranking hanging by a thread

Nothing less than victory will suffice for Australia in the third Test in Colombo if they're to escape from their shock series defeat in Sri Lanka with their world No.1 ranking intact.

Even then, Steve Smith's side will have to hope for an intervention from Mother Nature or a shock result in the Caribbean, and a Pakistan fightback in England in order to avoid slipping from top spot on the ICC Test Championship ladder.

The Australians have held the No.1 position for less than six months; they regained the title they had lost in August 2014 in February this year following a 2-0 series triumph in New Zealand.

At the time, captain Smith saw it as merely a step in the right direction as the Australians set themselves some lofty goals.

"It is a good start for us," he said. "We want to win every series that we play.

"We were able to adapt to these conditions really well ... hopefully we can do that when we play that next Test tour."

Unfortunately for Australia, that next tour was this trip to Sri Lanka, where the men in Baggy Green were heavily favoured against a nation ranked seventh in the world.

Yet despite setting themselves for the task of a first series win in Asia since their last trip to Sri Lanka in 2011 with an exhaustive preparation that appeared to leave no stone unturned, the tourists have been completely outplayed in the opening two Tests to spectacularly surrender the series.

From four innings, they've mustered a best of 203, with Smith's second-innings 55 in Kandy the only milestone achieved.

The theme of the series has been Australia's frailties against spin bowling, and the Sri Lankan spinners' particularly impressive demonstrations of their art.

As a consequence, Australia look destined to slide down the ICC Test Championship rankings.

In order for them to stay number one, the following three things have to happen:

• Australia must win the third Test against Sri Lanka
• India must fail to win either the third or the fourth Test against West Indies
• England must fail to win the final Test against Pakistan

If Australia beat Sri Lanka in the third Test, they will move to a 111 rating on the ICC Test Championship ladder.

India can move to a 112 rating if they beat West Indies in the third and fourth Tests to claim the series 3-0.

Likewise, England would move to a 112 rating if they beat Pakistan in the final Test of that series.

However, should Pakistan happen to beat England in the fourth Test, and the above scenarios play out with Australia's and India's respective series, Misbah-ul-Haq's side would leapfrog both England and India and draw level with Australia on a 111 rating – slotting into second place only on fractions of a point.

It all means Australia have plenty to play for in what is – at least in the context of the series – a dead rubber Test.

"It means a hell of a lot," Mitch Marsh said of the Test Championship ladder. "It's what we strive for.

"In the Test arena you don't play for a premiership, you play to be number one in the world.

"Any team that gets knocked off the perch as number one Test team in the world, it would certainly hurt everyone."