Muhammadu Buhari's All Progressives Congress (APC) party retained control of the southwestern state and commercial capital, shoring up the new administration's power after last month's delayed presidential polls.
Lagos is a crucial region to control within Nigeria, as the city of an estimated 21 million generates up to one third of Nigeria's total economic output. The state's economy is roughly double the size of Kenya's. The result means that for the first time since 1999, the same party will hold Lagos and the presidency.
Reports on the precise tallies differed, but broadly concurred that Akinwunmi Ambode of the APC took roughly 100,000 more votes than Jimi Agbaje of the People's Democratic Congress (PDC) in the key battleground state.
The PDC is the party of outgoing President Goodluck Jonathan, defeated by former army general Buhari last month.
Unlike that ballot, marked by record turnout, observers said on Sunday that voters did not mobilize en masse for the regional elections. Fears of violence at the polling station, which proved justified in some cases, mixed with voter apathy, were cited as reasons for keeping people at home.
Threats of violence from Islamist militant group Boko Haram had prompted the delay of the presidential poll, and more than a dozen people were killed in attacks during that campaign. However, one monitor said that the violence was worse this weekend around the country.
"I think it was worse than the presidential vote … we've had more reports of fights and skirmishes around polling areas," Reuters quoted Clement Nwankwo, executive director of the Policy and Legal Advocacy Center, as saying.
The oil-rich state of Rivers in the Niger Delta was particularly tense. There, Governor Rotimi Amaechi had been feuding with President Jonathan ever since defecting from the PDP to Buhari's APC two years ago.
The start of voting was delayed; a large protest took place in the state capital Port Harcourt, shootouts hit several towns, electoral commission property came under attack and some reports suggested that ballot boxes were snatched. Amaechi called the vote a "sham." In some parts of the state, voting was canceled.
Two weeks ago, in the presidential polls, Jonathan's PDP had won with more than 95 percent of the Rivers vote, prompting Amaechi's spokeswoman to accuse the rival party of a massive ballot-stuffing campaign.
Across the country, at least 10 people were killed in election-related violence on Friday and Saturday, including a politician from Jonathan's PDP, who was shot in his home, according to police.
The APC logged other gains in Kaduna and in Buhari's home state of Katsina, seemingly boosted by the presidential win.
Overall the Independent National Electoral Commission reported 66 instances of violence at polling stations, with the highest numbers in Rivers and other southern states.
msh/cmk (AFP, Reuters)