Rio polled 71,3372 votes to defeat his nearest Congress rival K V Pusa by 40,0225 votes.
Akhei Achumi of Social Party (India) polled 9,695 votes, while NOTA had 2,696 votes. Another 189 votes were rejected, said Returning Officer for Nagaland Temjen Toy.
Declaration of result in Nagaland was delayed as two EVMs were defunct and data could not be retrieved.
This was the third straight win for the ruling Naga People's Front in Lok Sabha polls.
"My winning margin does not matter as I will be going to Delhi for the bigger cause of the Naga people," he said.
Being a pre-poll ally of BJP, Rio said "I have already had a conversation with Narendra Modi and conveyed that proper discussions would be held only after meeting him in Delhi tomorrow."
Meanwhile, Nagaland Congress president S I Jamir said "We cannot expect good results on our part as it was not an election in the true sense, but only a money game."
"The Congress will never let the people down and will continue to fight communal forces in the interest of people of the state," Pusa added.
