About 10 per cent polling was recorded in Jayangar Assembly segment till 9 am, poll officials said.
The Karnataka Assembly election was held on May 12 but in Jayanagar the poll was countermanded following the death of BJP candidate B N Vijayakumar, who was holding the seat.
The BJP has named B N Prahlad, brother of Vijaykumar, as its candidate.
The Congress has fielded senior party leader and former Minister Ramalinga Reddy's daughter Sowmya Reddy as its candidate.
Just days ahead of polls, the Janata Dal(S) had on June 5 pulled out its candidate and extended the party's support to its ruling coalition partner, the Congress.
JD(S) supremo H D Deve Gowda had announced that his party candidate Kalegowda was "retiring" from the contest, and they would support Congress' Sowmya Reddy.
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Both the Congress and JD(S) had fielded candidates against each other, despite being coalition partners, in the recent election to the Rajarajeshwari Nagar Assembly seat in the city.
Congress candidate Munirathna had won the seat, relegating the JD(S) candidate to a distant third.
Over two lakh voters are expected to cast their votes in about 216 polling booths in the Jayanagar constituency today, where about 19 candidates are in the fray.