Abdullahi, the PDP senatorial candidate, lost to Mallam Saliu Mustapha, a former APC national chairmanship aspirant.
According to the former minister, the preliminary review of the results "shows substantial irregularities and manipulations that are inconsistent with the provisions of the electoral law."
APC defeated their PDP counterparts in a clean sweep of all the 9 national assembly seats in the state after the announcement of results by INEC on Sunday.
But in separate statements Monday night, the PDP while urging members to remain calm, promised to challenge the result in court to "reclaim their mandate".
Candidates who also rejected the results include Rafiu Ibrahim, the party's Kwara South senatorial candidate.
He said there "were several reported cases of gross electoral malpractice and widespread electoral fraud that marred the process.
"A team of lawyers are already studying the results and would be taking appropriate legal steps", he added.
Others are Abdulwahab Isa, the party's reps candidate for Ilorin East/Ilorin South, Dare Bankole and Ibrahim Ajia, Ekiti/Oke-Ero/Isin/Oyun and Ilorin West/Asa house of representatives candidates respectively.