In results declared early yesterday, the Democratic Unionist Party led with 28 seats, just one more than Sinn Fein's total.
At stake in the outcome from Thursday's snap election is the revival or demise of power-sharing between Irish Catholics and British Protestants, the central objective of the US-brokered Good Friday peace accord nearly two decades ago.
Sinn Fein was seeking to overtake the Protestants of the Democratic Unionists and become the No. 1 party for the first time in Northern Ireland an achievement that would have given Sinn Fein the right to the top government post of "first minister."
O'Neill, the daughter of an Irish Republican Army veteran with childhood memories of the conflict that claimed 3,700 lives, represents a leadership shift within Sinn Fein to the first post-war generation following the IRA's 1997 cease-fire and 2005 disarmament.
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Friday's final Northern Ireland-wide total of first-preference votes the core measure of party popularity showed the Democratic Unionists narrowly on top with 28.1 per cent, down 1 point from the last election 10 months ago. Sinn Fein trailed with 27.9 per cent, up 4 points, the narrowest sectarian gap in Northern Ireland electoral history.
Voter turnout reached nearly 65 per cent, 10 points higher than last year. Former Deputy First Minister Martin McGuinness triggered the election by resigning in January, declaring the vote a referendum on Foster's leadership. McGuinness, a former IRA commander recently diagnosed with a rare and often fatal disease, didn't seek re-election.