Leaders said an announcement of Felix Tshisekedi's (pictured above) victory did not reflect the findings of their 40,000 observers who monitored results posted at each polling station.
The secretary general of DRC's Catholic Church would not reveal who won the vote but, according to diplomats briefed on the results, rival opposition candidate Martin Fayulu won by a comfortable margin.
Donatien Nshole also called for peace as he urged those challenging the official announcement - which had previously been delayed - to do so without violence and within the country's legal framework.
While backers of Mr Tshisekedi took to the streets of the capital Kinshasa in celebration (pictured below), supporters of Mr Fayulu denounced the result as fraudulent.
According to observers and diplomats, DRC's outgoing President Joseph Kabila seems to have reached a deal with Mr Tshisekedi to stop Mr Fayulu (pictured below) - an outspoken critic of corruption - from winning.
Speaking earlier this week, a Kinshasa-based worker from the Catholic aid charity CAFOD told Premier a fraudulent result could trigger unrest in DRC.
Bernard Balibuno said: "We are really afraid that, if the person who is announced the winner is not what the people have voted for, this may create issues in the county."
Click here to listen to Premier's Alex Williams speaking with Bernard Balibuno via telephone from Kinshasa, DRC:
Stay up to date with the latest news stories from a Christian perspective. Sign up to our daily newsletter and receive more stories like this straight to your inbox every morning.