Lawyer Kipchumba Karoli has rejected the ongoing tallying of results which indicates Governor Jackson Mandago is likely to win the UDA Senate ticket in Uasin Gishu.
Karoli is claiming massive rigging of votes by his rival and says his lawyers have written to UDA party over the matter.
He alleges that by last evening, he was leading in the vote tally but last night, figures were altered.
"We are aware that last night more than Sh6 million was used to alter figures in areas where I had a clear win, we do not accept such doctored results," Karoli said
Mandago's team immediately dismissed the claims as false.
In the preliminary results, Mandago appeared headed for victory as vote counting continued.
Mandago is vying for the Senate ticket and Karoli took an early lead in some polling stations but was later edged out as counting continued.
Mandago is completing his final term as governor and many expected him to win easily but with more than a third of votes so far counted, he appeared poised for a narrow victory.
Karoli is a newcomer in Uasin Gishu politics and carried out quiet campaigns in the county.
In preliminary results, Mandago had more than 27,000 votes closely followed by Karoli at about 20,000 votes
Vote tallying is however still going on in the region.
In the race to succeed Mandago, politician Jonathan Bii was neck to neck with former envoy Julius Bitok in results streaming in from most polling stations.
Bitok led in the Kesses constituency while Bii is ahead in Soy sub-county.
In the race for parliamentary tickets, Kapseret MP Oscar Sudi has a comfortable lead against his rivals.
Speaker for Uasin Gishu David Kiplagat was leading in Soy constituency while newcomer Phillis Bartoo took lead in Moiben constituency.
In Kesses constituency, it's a tight race between former speaker Isaac Terer and former finance executive in Uasin Gishu Julius Rutto.
In neighbouring Elgeyo Marakwet, Deputy Governor Wesley Rotich took an early lead in the race for governor ticket.
He is followed closely by former IG Joseph Boinnet.
WATCH: The latest videos from the Star