Though there are 23 candidates in the fray for the April 17 poll, the real fight will be between Chavan and Patil.
There are six Assembly segments in the Nanded LS constituency and all are held by Congress. Chavan represents the Bhokar seat in state Assembly.
There were reports that the announcement of Chavan's candidature was delayed as the Congress leadership weighed the "winnability" factor against the negative publicity which he got in Adarsh Housing Society scam.
Chavan was first elected to Lok Sabha from Nanded in 1987 but was defeated in 1989 poll by a Janata Dal candidate.
Nanded has always been his bastion. His father late S B Chavan, in his stint as chief minister and Union minister, had initiated many development projects in the district.
BJP candidate Patil says, "There is both a pro-Modi wave and an anti-Chavan wave."
Patil won the seat in 2004 and later joined the Nationalist Congress Party (NCP) before returning to BJP.
There are six Muslim candidates in fray in the constituency having 13 per cent population from their community.
Nanded is famous for the Hazur Sahib Gurudwara, the place where tenth Sikh guru breathed his last and attracts lakhs of pilgrims every year.
Chavan dismisses the opposition campaign against him on Adarsh as "political conspiracy" to tarnish his image. After Chavan came in for flak over Adarsh, the party was toying with the idea of fielding his wife Ameeta, but dropped the plan as it would have been a close finish with the BJP candidate.
Adarsh is a high-rise building in south Mumbai which, while meant for serving retired defence personnel, led politicians, bureaucrats and defence officials to circumvent rules in return for apartments for themselves and relatives.
Three of Chavan's kin were said to have been allotted flats in Adarsh. In the wake of the scandal, Chavan was forced to resign as chief minister in 2010. A judicial probe later indicted Chavan and two of his predecessors, Vilasrao Deshmukh and Sushilkumar Shinde, among others. The report was rejected by the Maharashtra government.
Chavan got a reprieve when the Central Bureau of Investigation did not name him in a supplementary charge sheet pertaining to the scam after Maharashtra governor K Sankaranarayanan refused to allow CBI to prosecute him.
Sitting MP in Nanded, Bhaskarrao Patil Khatgaonkar, married to Chavan's sister, has made way for the former CM.
Chavan's father was elected twice to the Lok Sabha from Nanded and served as finance minister and Home minister at the Centre, besides being Maharashtra CM twice.
Nanded was among Modi's campaign stops.
Winning the election will help Chavan reclaim his reputation as one of the Congress's top leaders in the state.
Political observers feel that despite Modi rally, the Maratha leader has a good chance of entering Lok Sabha once again.