The BJP last won an Assembly seat in West Bengal in a bypoll in 1999 when it was an ally of the Trinamool Congress.
The party has two Lok Sabha seats in the state.
BJP state general secretary Samik Bhattacharya won the tough fight in the former Left stronghold of Bashirhat Dakshin in North 24-Parganas district -a mix of urban and rural areas bordering Bangladesh - by a slender margin of 1,586 votes.
After the counting of all the rounds it was found that Bhattacharya had won by a margin of 1,742 votes but one EVM could not be opened and it was sent to the EC for counting.
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The TMC demanded counting of the votes in that EVM before declaring the result and after it was done the margin came down to 1,586 votes.
After his win, Bhattacharya told reporters, "It is not my victory, it is the victory of the masses who feel that the BJP can only take on the TMC's misrule in Bengal and give them justice."
In Chowringhee where the BJP made an all-out effort to defeat the TMC with its national president Amit Shah himself jumping into the campaign bandwagon, TMC's actor-turned politician Nayana Bandyopadhayay won by a margin of 14,344 votes.
Nayana, wife of senior TMC leader Sudip Bandyopadhaya, leader of the TMC parliamentary party, secured 38,328 votes while BJP's Ritest Tiwari bagged 23,984 votes.
TMC all-India general secretary Mukul Roy said that the BJP was ahead of TMC by 30,223 votes in this Assembly segment in the Lok Sabha polls and the party had been able to narrow down the margin over 28,000 within four months.
"Despite this, people have repeatedly shown that they don't believe these and have reposed their faith in Mamata Banerjee," he stated.