By Kevin Mwanza

NAIROBI (Reuters) - Kenya's defeated presidential contender Raila Odinga has delayed filing a legal challenge against his election loss, his allies said on Friday, extending a period of uncertainty over the disputed poll.

Odinga refused to accept last week's slim first-round win by rival Uhuru Kenyatta - and his allies had said he would file a petition to the Supreme Court alleging collusion between the president-elect and the electoral commission on Friday.

But officials from Odinga's CORD coalition told reporters the papers would go to the court a day later on Saturday to prevent the complaint getting "mixed up" with other election-related issues before the judges.

"The reason for the postponement is merely strategic and has nothing to do with the content of the petition and other accompanying documents," senior CORD member James Orengo told a news conference.

Kenyatta, the son of the country's founding president, faces charges of crimes against humanity at the International Criminal Court, alleging he incited violence during the bloody aftermath to Kenya's 2007 presidential vote. He denies the charges.

There has been no repeat of the deadly tribal clashes that convulsed Kenya after Odinga contested that result in 2007. Odinga has called for calm while he challenges the outcome of last week's vote and has said he will accept the court's ruling.

Kenyatta only just avoided a second round in last week's poll after winning 50.07 percent of the vote - candidates need more than half of all votes cast to win outright.

(Writing by Richard Lough; Editing by Andrew Heavens)