India's decision to field Shashi Tharoor for the post of UN Secretary General and his subsequent withdrawal has come in for critical comment in some quarters but Prime Minister Manmohan Singh sees no reason for being disheartened.

Pointing out that this was the first Indian challenge to the existing international order, Singh feels the future will have to reckon with the fact that India is ready to assume its rightful role in the management of international system.

"I have already said that this is a Herculean task and we are up against the existing international order," he said while returning from South Africa after a four-day trip Tuesday night. The prime minister said Tharoor's performance had been "very very creditable" even though he did not make it to the top post of the world body.

Tharoor, UN Under Secretary General of Communications, opted out of the race Tuesday after being in the second position in all the four 'straw polls'.

Significantly, one of the Permanent Members, believed to be the US, voted against him, signalling that his candidature could face a veto.

"I think there is no reason for being disheartened," Singh said. There has been criticism by some sections of the government's decision to field Tharoor.