Congress' Kalale N Keshavamurthy defeated his nearest rival V Srinivas Prasad (BJP) by over 21,000 votes in Nanjangud.
In Gundlupet, Geetha Mahadevaprasad (Congress) trounced BJP's C S Niranjan Kumar by over 10,000 votes, an election official said.
Both the seats were held by the Congress.
With the Assembly polls slated to be held in about a year, the Congress and the BJP had played for heavy stakes in the bypolls.
The by-elections were necessitated in Gundulpet following the death of Cooperation Minister Mahadevaprasad while in Nanjangud, it was caused by the resignation of Srinivas Prasad as Congress MLA after he was dropped from the ministry.
Geeta is the widow of Mahadeva Prasad.
Remaining neutral, former Prime Minister H D Devegowda- led JDS had not fielded its candidates.
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