Indian National Lok Dal (INLD) chief Abhay Chautala is leading by more than 2,000 votes over BJP-JJP candidate Gobind Kanda and Congress' Pawan Beniwal after three rounds of counting.
There are 16 rounds of counting before the official results are declared.
The election on October 30 saw a voter turnout of over 81 per cent for the high-stakes triangular contest among the INLD, the BJP-JJP alliance and the Congress.
The bypoll was necessitated with the resignation of Chautala from the seat in January in protest against the three agricultural laws.
After winning the by-poll in 2010, Abhay retained the seat in 2014 and 2019.