Starehe MP Maina Kamanda has conceded defeat and opted to support his rival Charles Kanyi, aka Jaguar.
Mr Kamanda has also said he will not ditch the Jubilee Party even though he claimed the nominations were a sham.
"I have been in this game of politics in Nairobi for close to 40 years now. There were other people before me...and these are the people who mentored me into politics in Nairobi and I have been the longest-serving leader of Nairobi and I am a strong supporter of Jubilee.
"What we went through on April 26 was an internal mechanism of the party so we could get a candidate. I have been very vocal that even those who lose in Jubilee nominations should not leave the party and you have quoted me on that.
“For that reason I am not prepared to leave the Jubilee Party,” said the MP.
He said there had been issues with the party headquarters over the manner in which the nominations were conducted.
According to him, non-party members were allowed to take part in the exercise that he said was a sham.
“Fifty per cent of those who voted in Nairobi were members of ODM. So it was like an ODM nomination,” he said.
He urged his supporters to throw their weight behind Mr Kanyi on August 8.
Mr Kamanda said three of his supporters were hospitalised because of shock.
But as he declared his support for Mr Kanyi, he accused Jubilee of "pushing out the old guard".
"We need to be told if the old people have space in the party. I won the nominations but someone else was given a certificate," he said.