Senior Congress leader Randeep Singh Surjewala lost by a margin of 567 votes over the ruling BJP's Leela Ram.
Surjewala was seeking re-election from Kaithal constituency.
Despite series of defeat, the incumbent MLA from Kaithal entered the poll fray. While Surjewala was earlier an MLA in Narwana, he switched to this constituency in 2014.
The BJP, which had set a target of winning 75 seats ahead of the polls, is leading in 38 seats, while the Congress is ahead in 32 constituencies. The fledgling Jannayak Janta Party, which fought its maiden assembly polls, is also ahead in 10 seats.
If the trends hold, the JJP could likely emerge as the kingmaker and hold the key to formation of the next government.
In what appears to be a setback to the BJP, seven of its ministers, assembly Speaker and state party chief are trailing.
The ministers include Ram Bilas Sharma, Capt Abhimanyu, O P Dhankar, Kavita Jain, Krishan Lal Panwar, Manish Grover, Krishan Kumar Bedi.
Speaker Kanwar Pal, a BJP legislator from Jagadhri, and state BJP president Subhash Barala, who is seeking re-election from Tohana, are also trailing, according to the trends.
Among the sportspersons fielded by the BJP, former Indian hockey captain Sandeep Singh and wrestler Babita Phogat are leading, while wrestler Yogeshwar Dutt is trailing.
