Loss of face would mean loss of control
If neither candidate musters a majority of the 1,200 or so votes, a re-election will be held two months later.
"They (Beijing) don't want to do it again in May because this would be a loss of face," said political analyst Willy Lam.
"If neither of the two candidates can get the 600 votes, it means that Beijing has lost control."
Opinion polls suggest Tang only has around 20 per cent support. Given a choice, however, more Hong Kong people seem to be demanding a fresh poll with fresh candidates.
The opposition Democratic camp and pro-business Liberal Party, which directly hold around a fifth of seats on the election committee, are planning to spurn both candidates and cast blank ballots in a bid to torpedo proceedings.
More may follow.
"The most important thing is we have doubts of the integrity of both candidates and so we believe the responsible thing to do is not to forcefully vote for one," said Selina Chow, a senior member of the Liberal Party and a former government adviser on the city's Executive Council.
Nagging rumours of Leung's underground Communist Party membership -- which he has denied -- and an ambiguous ideological stance have unnerved some in Hong Kong, where civil rights and freedoms are cherished.
Tang admitted on Wednesday that Leung may now have a winning chance, but declined to comment on whether Beijing officials are supporting his opponent.
Tang still enjoys support from less hardline Chinese factions and the business establishment -- another major force in Hong Kong -- including Asia's richest man, Li Ka-shing, and other tycoons.
Political currents drifting in favour of Leung don't leave him immune to a large-scale public backlash following Sunday's poll if he wins.
Thousands are expected to demonstrate on election day, including civic, student and pro-democracy groups, no matter who wins.
"He'll have a very hard time," the election committee member said of Leung. "He'll face a very hostile democratic opposition, a relatively hostile public ... and he'll face a very hostile civil service. So it will not be a honeymoon period for him."