Mamata took her one-to-one formula to Sonia in the hope that the Congress would facilitate direct fights in all states and avert a division in the anti-BJP votes.
"I told her the country wants it to be one-to-one in 2019. Jo party jahan strong hai wahan usko ladna chahiye (the party that is strong in a particular place should contest from that place). We want the Congress to help the regional parties' front that is being talked about so as to facilitate a one-to-one fight. This one-to-one fight will eliminate the BJP politically," Mamata told reporters outside 10 Janpath after meeting Sonia.
The Trinamool Congress leader also met a host of other opposition leaders during her two-day visit to the national capital. She is in Delhi to hold talks with various parties in a bid to form a united front against the BJP and bring together opposition parties on one platform.
Arun Shourie, Mamata's former cabinet colleague in the Atal Bihari Vajpayee government, deconstructed the formula after meeting the Bengal chief minister earlier in the day.
"If this one-to-one formula is adopted, the Opposition starts with 69 per cent of the votes. Even at the height of his popularity, Modi got only 31 per cent of the votes," he said.
Mamata has been pushing the one-to-one line, eager to ensure that the Congress does not bargain for a bigger piece of the pie when parties get down to putting together a coalition in some form. Although few seem interested in a pre-poll national alliance, there is a general consensus on pooling resources to reduce the BJP's numbers.
Shourie quoted Mamata as saying that in each state, the election coordination should be left to the strongest party there.
Asked if the Congress would support the idea of a "federal front", Shourie expressed the hope that the party would realise the need for everybody to be together.
"If this momentum (of the BJP) is not broken, there will be no Congress or any other party left after this," he said.
Shourie appreciated Rahul Gandhi's decision in forming the mahagathbandhan in Bihar while criticising him for refusing to accept Mamata's suggestion for a united fight in Tripura.
Asked about the Modi government, Shourie said: "Real control of the government and the party is slipping from Modi's hands into Amit Shah's hands, and the country will pay for this."
(With inputs from The Telegraph Calcutta)