Raju Shetty of the non-descript Swabhiman party dealt a double blow to the NCP, humbling another party candidate Nivedita Mane from the neighbouring Hatkanangle constituency.
Mandlik, sitting NCP member of Parliament, had openly rebelled against party president Sharad Pawar after being denied ticket for Kolhpaur seat and contested as an independent supported by the Left parties.
The NCP had fielded Sambhajiraje Chhatrapati, a descendant of Shivaji Maharaj, in place of Mandlik.
Mandlik's victory is being seen as a setback to Pawar, who had made the Kolhapur seat an issue of prestige, after Mandlik launched a bitter attack on him alleging that the NCP president was practicing a "use and throw" policy, humiliating honest party workers.
In his hectic electioneering, Pawar had found time to address as many as 18 meetings to appeal to voters to defeat Mandlik, a five-time MP from Kolhapur.
After his victory Mandlik said he would never ally himself with Pawar in the future and would work for farmers.
The NCP received another jolt in the defeat of Nivedita Mane by Raju Shetty who has floated the Swabhiman party to champion the cause of farmers in the region.
Mandlik and Shetty defeated their NCP rivals by a margin of over 44,000 and 95,060 votes respectively.