Early results in Nigeria’s presidential and parliamentary elections have put the ruling party’s candidate well ahead, but also revealed a surprise victory for the outsider Peter Obi in Lagos, the country’s biggest city and commercial powerhouse. Analysts speak of a “bellwether” election that could be a crucial turning point for Nigeria after several years of worsening insecurity and acute economic troubles. Many believe a credible poll and progress in tackling the country’s multiple problems are key to stability across a swath of Africa. Eighteen candidates hoped to replace the outgoing two-term president, Muhammadu Buhari, but only three are considered to have a credible chance of winning power: Bola Tinubu, from the ruling All Progressives Congress (APC); Atiku Abubakar, of the main opposition People’s Democratic party (PDP); and the Labour party’s Obi. “What Obi has done is pretty mind-boggling. He has disrupted the duopoly of two behemoths, two very rich and very powerful parties,” said Prof Abiodun Adeniyi at Baze University, Abuja. Tinubu, 70, and Atiku, 76, are seen as traditional politicians representing Nigeria’s established political elite. Obi, 62, is considered a reformist who has reached across the country’s faultlines to woo voters from all communities and run a slick social media campaign to attract young voters. Provisional results from the Lagos state collation centre released on Monday gave Obi, who switched to the tiny Labour party from the PDP last year, a narrow win over Tinubu, with 582,454 votes to 572,606. “The results in Lagos are pretty extraordinary,” said Adeniyi. “It’s a sign of the fatigue Lagosians have with Tinubu, who has held the state for the last 20 years. Obi is coming from a distant place and … has shown his message of change resonates with Nigerians.” Tinubu did appear to have won at least two other states with some ease, though Obi has done well in his power base in the south-east and made inroads elsewhere. The PDP is expected to hold on to most of its bastions, early reports suggested. Officials from the APC said on Sunday night that their own information showed that “Obi-dients”, as supporters of Obi called themselves, were likely to be disappointed. “Our candidate is coasting to victory. There is no pathway to Aso Rock Villa [the official residence and office of the Nigerian president] for Obi at the moment,” one senior ministerial aide told the Guardian. This may not concern Obi too much, however, some observers say. He has made massive gains and the four years before the next election would allow him to build the political organisation necessary for victory. After news of the defeat in Lagos, Tinubu issued a brief statement calling for calm. “As a democrat, you win some, you lose some. We must allow the process to continue unhindered across the country while we maintain peace and decorum,” he said. Nigeria’s electoral commission is not expected to name an outright victor in the race to succeed Buhari for several days. Technical problems with a new electronic voting system meant only a fraction of votes cast on Saturday had been collated. The multiple delays, incidents of disruption and technological problems with the new voting system have prompted fierce criticism. Yiaga Africa, a coalition of civil society groups, said it had concerns about “voter suppression and irregularities”. Independent observers on Monday issued a statement saying the election “fell well short of Nigerian citizens’ reasonable expectations” but praising voters’ “extraordinary resilience and resolve to have their voices heard through the ballot”. Though no reliable counts are yet available, some early estimates suggest there was high turnout, which would be expected to deliver a boost to Obi, who is popular among young people, who make up about a third of the 87 million eligible voters. However, in Lagos only a relatively small proportion of eligible voters cast their ballots. Though the contest looks close, Nigerian electoral law makes a runoff unlikely as the winning candidate needs only a plurality of votes, provided they get 25% of the vote in at least two-thirds of the 36 states. Nigeria is contending with multiple intersecting crises including economic turmoil, extremism and criminality affecting much of the country. In recent weeks, an effort to replace almost all Nigeria’s banknotes – in part to reduce the widespread practice of vote-buying – has caused massive economic disruption and much popular anger. However, analysts point out this is the seventh poll held since the end of military rule in 1999 and that some Nigerian democratic institutions are growing stronger. That none of the main candidates are former military officers – a first for a Nigerian poll – is also viewed as an achievement. The decision of Buhari, 80, to respect the constitutional two-term limit has also been cited as a positive sign.