New Delhi: The Supreme Court today refused to stay BJP leader B S Yeddyurappa's swearing-in as Karnataka chief minister after a rare post-midnight courtroom battle unfolded dramatically over the Congress-JD(S) combine's legal push to stall the government formation.

After a nearly three-and-a-half-hour hearing beginning 2:11 AM, a three-judge apex court bench also made it clear that the swearing-in and the government formation would be subject to the final outcome of the case before it.

The order came hours before the swearing-in ceremony in Bengaluru, where 75-year-old Yeddyurappa is slated to become chief minister of the state for the second time, even as the Congress-JD(S) combine has been claiming a majority with support of 117 MLAs, against BJP's 104.

The bench, comprising justices A K Sikri, S A Bobde and Ashok Bhushan, posted the matter for further hearing tomorrow morning and ordered placing before it the letter of support from MLAs presented by the BJP to Karnataka Governor Vajubhai Vala while staking claim to form the government.

The bench said it will peruse the letter as it was necessary to decide the matter. It also issued notices to the Karnataka government and Yeddyurappa.

"As far as swearing-in is concerned, we are not restraining it, but we are making it subject to the outcome of the case," the bench said.

Just before the bench was to dictate the order, Congress leader and senior advocate Abhishek Singhvi pleaded with the bench not to dictate the final order and sought to argue the matter further.

He said the BJP has 104 MLAs and the governor invited Yeddyurappa to form the government in an "unconstitutional manner".

In his submission, Singhvi said the swearing-in could be extended from 9.30 AM to 4.30 PM on Thursday and the BJP should be asked to produce the letter of support from majority of MLAs.

The bench, which was constituted post-midnight by Chief Justice of India Dipak Misra on the Congress-JD(S) plea for an urgent hearing, sought to know can it restrain the governor from inviting a party to form the government, to which Singhvi said the Supreme Court had done so in the past.

The court, during the hearing, also asked was it not a convention that the single-largest party gets invited by governor to form government and prove majority.

The bench wondered whether the Supreme Court's restraining order against the government might lead to a constitutional vacuum in the state.

It also observed that the general trend of its past judgements was not to issue injunction or restrain the governor.

The bench observed that it was preposterous to argue that the MLAs, before they take oath, were not amenable to anti-defection law and meant an open invitation to horse-trading.

It also sought to know why the governor gave 15 days for floor test to the BJP and how it was claiming majority when the Cong-JD(S) combine had higher numbers.

Appearing for the Centre, Attorney General K K Venugopal said the swearing-in was subject to the outcome of floor test and the court can hear the matter after that.

With Singhvi arguing that the Constitution gives immunity to the governor only for discharge of duties, the bench asked whether he wanted the court to scrutinise discretion of the governor when it does not have the letter of support given by the BJP.

Singhvi said the governor had negated democracy by not calling the alliance commanding majority.

"It is the biggest license to poaching if the governor gives 15 days to BJP to prove majority as in earlier such cases 48 hours were given by SC," Singhvi said.

Senior advocate Mukul Rohatgi, representing the BJP and Yeddyurappa, said no injunction can be issued to the governor and objected to hearing of the matter at midnight.

The joint petition by Congress' Karnataka unit chief G Parameshwara and H D Kumaraswamy had sought a stay on the oath-taking ceremony.

The Congress party termed the move to invite the BJP to form the government as an "encounter of the Constitution". On the other hand, the BJP, which emerged as the single-largest party in the just-concluded Karnataka polls, accused the Congress of trying to "loot the mandate" by seeking to stitch a post-poll alliance with the JD(S).

Amid intense jockeying for power and allegations of horse-trading, Vala had last evening invited Yeddyurappa to form the government and take oath as chief minister, prompting the Congress to move the Supreme Court accusing the governor of acting as a "stooge" of the saffron party.

Assigned the task to lead Congress' legal challenge against Vala's decision, Singhvi last night met the Supreme Court registrar to take forward the "urgent petition".

JD(S) leader Kumaraswamy has accused the BJP of luring his MLAs with Rs 100 crore bait, while outgoing CM Siddaramaiah of Congress alleged that Prime Minister Narendra Modi was encouraging "horse-trading" to ensure the BJP returns to power in the state despite falling short of a majority.