Mugabe was coy about endorsing anyone ahead of the election in which Mnangagawa, the former deputy that he fired, faced Chamisa, a 40-year-old lawyer. He indicated, however, that Chamisa was the only viable candidate.
"I cannot vote for those who have tormented me," Mugabe said in a reference to Mnangagawa, who took office with the military's support.
"I cannot vote for Zanu-PF."
Mugabe, who has backed a new political party that is part of a coalition supporting Chamisa, said of Chamisa: "He seems to be doing well at his rallies ... I wish to meet him if he wins." And he added: "Whoever wins, we wish him well ... And let us accept the verdict."
Mnangagawa said in a video posted on Facebook that Chamisa had "forged a deal" with Mugabe and that a vote for the Opposition leader amounted to an endorsement of the old order. "We can no longer believe that his intentions are to transform Zimbabwe and rebuild our nation," Mnangagawa said.
Chamisa, meanwhile, said at a news conference that he welcomed the vote of Mugabe and that "you don't discriminate against voters".
Many in Zimbabwe knew no other leader but Mugabe, who led the country for 37 years after independence from white minority rule in 1980. What began with optimism crumbled into repression of the Opposition, alleged vote-rigging, violent land seizures from white farmers and years of international sanctions.
Zimbabwe hopes that credible elections could get those sanctions lifted and bring badly needed investment for a collapsed economy.
- AP