Official results were to be announced on Friday afternoon but as polls closed on Thursday evening Bouteflika's representative Abdelaziz Belkhadem was declaring, "Our candidate has won."
"There's no doubt, Bouteflika has won a crushing victory," he said.
But former prime minister Ali Benflis cried foul and said he would not accept the result of the poll.
"I'm certain there has been massive, general and generalised fraud," he told RFI. "All kinds of fraud have been used, old methods and new methods."
About 70 people were injured when supporters of a boycott clashed with police on polling day, especially in the Berber-majority region of Kabylia, which has a long history of opposition to successive governments.
Turnout was low, even according to official figures that media and regime opponents claim are overestimates.
Nationwide 51.7 per cent of voters cast their ballots, officially, way below 2009's official 74 per cent, with 37 per cent in the capital, Algiers, and about 25 per cent in Kabylia.
Bouteflika has hardly ever been seen in public since he suffered a minor stroke last year.