Kajiado Governor David Nkedianye has told Jubilee nominee for governor race Joseph ole Lenku to prepare for a mother of all battles on August 8.
The former Interior CS clinched Jubilee's ticket for the Kajiado governor seat on Wednesday.
Lenku garnered 18,456 votes in party primaries on Wednesday, while his rival Tarayia ole Kores received 6,705 votes.
But Nkedainye dismissed Lenku's win saying he is "a known national failure".
"There is no way one can obtain 88,000 votes in party nominations in Kajiado. What his opponent (Kores) got reflects the true picture," he said on Friday.
He was speaking to teachers from the region.
"God forbid this one if elected. He will bring down this county in many ways. It is my prayer that the people of Kajiado see the light by rejecting him." the Governor added.
He described Lenku and his running mate as a "team of masqueraders wanting to clinch power from the back door".
"If (Lenku) failed to handle the docket in the Interior ministry, how do you expect him to manage the entire country and its huge budget? He is just a joker," Nkedianye said.
President Uhuru Kenyatta fired Lenku as Interior CS in 2014 after 36 Kenyans were massacred by suspected al Shabaab militants in Mandera.
Since announcing his bid for the county seat, Lenku has been the subject of criticism for Nkedainye, who seeks to defend his seat on an opposition ticket.
The county boss said his administration has rolled out many development projects since he was elected in 2013.
He also defended his administration, saying he has employed staff from each community living in the county.
"I have not discriminated any area in the region," he said, adding that all the communities in Kajiado support his re-election bid.
He expressed optimism that NASA will get a majority in the county assembly.
"This time round, I believe the people of Kajiado will get the right leaders," he said.