Mugabe's comments marked his first intervention into this tightly contested election.
After presiding over a precipitous economic decline and allowing his unpopular wife, Grace, to position herself as his possible successor, he had lost much of his clout within Zanu-PF.
His comments have likely come too late to have much effect on the vote.
But the nearly two hours he spent talking were a last stand of sorts for the ailing founder father of Zimbabwe.
He devoted most of his speech to criticising Emmerson Mnangagwa, who took the reins after the bloodless coup in November, which was supported by the military.
Tonight's vote pits Mnangagwa, 75, against Chamisa, a 40-year-old lawyer and pastor who would become Africa's youngest head of state.
"Thrust away the hypocrites," said Mugabe, who sat slouched in a green armchair. "Let tomorrow be the voice of the people saying we shall never again experience a period where the army is used to thrust one person into power."
He minced no words in calling November's events a coup, and lamented that regional governments like South Africa's that had once backed him have so quickly started working with Mnangagwa.
"Our neighbours have been fooled into believing that it was not a coup d'etat. Nonsense, it was a coup d'etat," said Mugabe.
Mugabe and his wife have been reclusive since November, mostly remaining in their mansion outside the capital, Harare, known as Blue Roof.
Grace Mugabe was present at the press conference, shielding herself from the sun with an umbrella emblazoned with a photo of her wedding day. She occasionally butted in, telling her husband to sit up straight and speak up.
When Mugabe brought up the issue of his pension, Grace stepped forward to clarify the amount: US$467,000.
"Can you imagine," she said, indignant that it's not larger. The average Zimbabwean makes less than US$2000 per year.
"There is no place for Grace Mugabe in my Government," said Chamisa, apparently seeing a ploy for a role for her should he win the election. Chamisa's press conference was totally overshadowed by Mugabe's.
"Deal with your old man," said Chamisa.
Mugabe said the notion that he had been planning to hand over power to Grace was "utter nonsense." He said he had intended to resign in December, and had spoken to former Defence Minister Sydney Sekeremayi about being his replacement.
Mugabe's criticism of military intervention in politics is one that most Zimbabweans would find more than a little sanctimonious. The military and Zanu-PF have always been closely linked, with generals often becoming ministers and a heavy army presence deployed at polling booths in previous elections.
In 2008, Mugabe lost the first round of an election to the MDC candidate. In the weeks between then and the run-off, more than 200 opposition supporters were killed and thousands, including journalists, arrested.
Recent polls have indicated that Zanu-PF and the MDC are neck-and-neck. Should neither side capture 50 per cent of the vote, a runoff will be held on September 8. MDC supporters and civil rights organisations have documented widespread intimidation and vote-buying, casting doubts on the credibility of the election.
Chamisa and Mnangagwa held their final rallies on Sunday, just over a mile from each other in Harare. There were tense standoffs between supporters who ran into each other afterward, but no violence was reported.
Both candidates have promised to open Zimbabwe up to foreign investment after years of isolation and sanctions that have contributed to crippling the economy, but an election broadly perceived as unfair would jeapordise readmission into the international community.
International election observers are in Zimbabwe for the first time since 2000, when Mugabe expelled them over perceived interference.
"So the election [today], I ask: Is it to bring democracy? To bring constitutionality? To bring freedom? Or shall we see the return, a return of the same rule we have experienced since November," said Mugabe. " Let us all pray that [today] brings us good news."
