Even though the election passed off peacefully, several water cannon trucks patrolled outside the central Harare headquarters of the opposition Movement for Democratic Change (MDC) as its red-shirted supporters danced in the streets.
Some local results from parallel parliamentary elections have been declared but the Zimbabwe Electoral Commission (ZEC) has yet to produce any figures from Monday's presidential vote.
ZEC chief Priscilla Chigumba said the presidential election result may not be ready until Saturday, Presstv reported.
Former MDC finance minister Tendai Biti and ZESN, the main domestic election monitor, said one in five polling stations - more than 2,000 in all - had not physically posted tallies on their doors, as required by law.
That omission gave room for the ZEC, which ZESN and the opposition have accused of bias, to manipulate the results in favor of President Emmerson Mnangagwa and the ruling ZANU-PF party, Biti said.
"There is a deliberate delay in formally announcing results," Biti told a news conference, characterizing it as "interference with the people's will."
ZESN and other civil society groups were preparing a legal challenge to force the results into the open, Biti said.
ZEC said there was no rigging or cheating in the vote, whose credibility is vital in Zimbabwe's attempts to emerge from the pariah status and economic decay into which it sank in the latter half of Mugabe's nearly four decades in charge.
However, ZEC did not explain the failure by the polling stations to post results.
The poll is a two-horse race between 75-year-old Mnangagwa, a long-serving security chief who took over after Mugabe's removal, and 40-year-old MDC leader Nelson Chamisa.
Both men have expressed confidence in victory although Western diplomats and local observer groups said the race, which saw a turnout of 75 percent, was too close to call.
"The information from our representatives on the ground is extremely positive!" Mnangagwa said on his official Twitter feed.
As well as electing a president, Zimbabweans were voting for 210 members of parliament and more than 9,000 councilors.
The final outcome may not be known until Aug. 4. In the absence of a clear winner, a run-off will be held on Sept. 8.