After the music and the singing and the long weeks of campaigning, after the shouts of “power to the people” and “Viva”, President Emmerson Mnangagwa made a final appeal to the people of Zimbabwe on Saturday.

“We are reaching the end of a long road and are at the beginning of a new era,” Mnangagwa told the crowd in the national stadium on the outskirts of Harare, the capital. “What is wanted now is one push to have the most thunderous victory in the history of this country.”

Early on Monday, polls will open in the first election since Robert Mugabe’s 37-year rule was ended by a military takeover nine months ago. The vote will determine the future of the former British colony for decades.

The poll pits Mnangagwa, the 75-year-old stalwart of the ruling Zanu-PF party, who succeeded Mugabe, against Nelson Chamisa, a 40-year-old lawyer and pastor who leads the Movement for Democratic Change (MDC), Zimbabwe’s main opposition.

The most recent published survey put Mnangagwa, a dour former spy chief and aide of Mugabe known as “the Crocodile”, three points ahead of Chamisa. Zanu-PF’s internal polling suggests a wider margin, but one which is still too close for the ruling party to be comfortable.

Saturday’s rally was supposedly the climax of the Zanu-PF campaign – but it cannot have reassured party strategists. Even with the considerable organisational power of the party fully deployed, the stadium was far from full, applause was desultory, and hundreds were pouring through the exits before the president’s speech was over.

The opposition is confident of victory. At a noisy rally last week in Chitungwiza, a satellite town of Harare, Chamisa told supporters the stakes were high. The “elderly” Mnangagwa should step aside for a new generation and a new style of politics, Chamisa told the Observer as he came down from the podium. “Zimbabwe does not need a big man,” he said – a reference to the autocrats across Africa who rule for decades – but “a big idea”.

Zanu-PF supporters at the rally. Photograph: Dan Kitwood/Getty Images

Chamisa’s words have a resonance and relevance in his own country and beyond. In Ethiopia, a new 42-year-old prime minister’s spectacular reforms and promise of multiparty democracy has inspired many more living elsewhere on the continent.

Across southern Africa, it is striking how many parties which came to power decades ago after winning liberation struggles against colonial powers or white supremacist regimes remain in charge many decades later.

In Zimbabwe, Zanu-PF has long claimed a right to rule based on its victory in the brutal wars of the 1960s and 1970s. Yet this heritage is a double-edged sword as the party tries to distance itself from the disastrous economic legacy of Mugabe’s misrule. Election videos have featured images of the guerrilla war but not of the former dictator, who led the party through the conflict before taking power.

Party loyalists argue that the dictator betrayed Zanu-PF and its principles. Constantino Chiwenga, the vice-president, said that the ruling party was “bigger than one man”.

“Individuals come and go. Zanu-PF is the people’s party. We fought for the liberation of this country. We have always had the masses at heart,” Chiwenga told the Observer at a rally in a dusty, desperately poor settlement on the outskirts of Harare.

A 61-year-old former general who led the military during the takeover last year, Chiwenga, like Mnangagwa, has been accused of involvement in widespread atrocities perpetrated by security forces in the 1980s.

The vice-president promised the small and subdued crowd free healthcare, a metalled road, better schools and sanitation. Zimbabwe’s once-famed infrastructure is crumbling and its economy is shattered. In the dusty shacks behind the neat lines of supporters, life is grim. “Life is horrible. Crime is bad. We have nothing: no school, no clinic, no jobs. They make promises and do nothing, “ said Joy Moyo, 28. “In November, when Mugabe went, we felt good, but so far nothing has been done. I’m very worried for my daughter. What will she have when she grows up?”

Such sentiments are widespread, but so is unease about the voluble Chamisa and the divided MDC. “Who knows anything about them? This young man, he talks so much,” said Memory Chila, 45.

Supporters of Nelson Chamisa at the opposition MDC’s final rally. Photograph: Mike Hutchings/Reuters

Previous elections during Mugabe’s rule were marked by systematic violence and intimidation of the opposition, as well as vote-rigging. Though the ruling party has benefited from a biased official media, support of traditional leaders and the manipulation of state handouts, few deny that these polls have been peaceful. Some MDC candidates call the calm “uncanny”.

Hundreds of international observers and media have been accredited, in a further break with the past.

Ministers deny the government’s desire to hold “free and fair” elections is rooted in anything but a fervent enthusiasm for democracy. Experts point out that whoever rules Zimbabwe will never get the huge loans needed to refloat the economy, attract investors, or satisfy the huge expectations of an increasingly restive population without the goodwill of the international community. This is contingent, as one observer puts it, on an “election that at least meets some basic standards”.

The most urgent question now is how the government will react if early indications show the opposition is close to victory on Monday, or if it becomes apparent during the count that Chamisa has won.

Some diplomats in Harare believe Mnangagwa will concede gracefully . But few analysts think Zanu-PF or the military will give up power easily.

“It is not beyond the realms of possibility that Zanu-PF will be the first liberation party voted out in this region … but it would be surprising. The party would be much happier dealing with the fallout of a flawed victory than defeat,” said Derek Matyszak, an analyst with the South-Africa based Institute for Security Studies. This opens the possibility of a protracted period of instability and protest as all sides appeal for overseas support – and to the streets.

Mnangagwa evoked a very different future in his speech on Saturday: a stable, prosperous, secure Zimbabwe ruled by the party that has held power for nearly four decades. “We will all build a united Zimbabwe together. Zanu-PF knows the history of the nation and Zanu-PF is going to continue the destiny of the nation,” he told the crowd in the stadium. But some were already drifting away.