Three-time winners and 2013 champions Nigeria edged past tournament debutants Burundi at the Africa Cup of Nations.
Second half substitute Odion Ighalo scored the only goal after 77 minutes in Alexandria with a curled finish past Burundi goalkeeper Jonathan Nahimana.
Burundi – the lowest-ranked side at the tournament – had struck the crossbar in the first half through defender Frederic Nsabiyumva’s looping header.
Guinea face Madagascar in the other Group B match later on Saturday.
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FC Midtjylland striker Paul Onuachu had Nigeria’s first real chance on goal after 12 minutes as his header forced Burundi goalkeeper Jonathan Nahimana in to action.
Burundi, 134th in the world standings, remained unfazed and Cedric Amissi’s close-range shot required a good save from Nigeria’s Daniel Akpeyi.
Arsenal’s Alex Iwobi and Villarreal 20-year-old Samuel Chukwueze offered the Super Eagles’ main attacking threat, but Gernot Rohr’s side were frustrated by a resolute and organised Burundi side – captained by Stoke City striker Saido Berahino – until Ighalo’s introduction.
The Shanghai Greenland Shenhua striker, formerly of Watford, produced a quality finish just four minutes after entering the field, following Ola Aina’s delightful back-heeled pass.
Nigeria were without striker Samuel Kalu, who had been taken to hospital after suffering from “severe dehydration” in training on Friday – a day after players’ union Fifpro had called for the tournament organisers to increase their planned number of heat breaks from two to four per match.
The Super Eagles now face Guinea on Wednesday (15:30 BST), while Burundi take on fellow debutants Madagascar on Thursday (15:30).
By BBC Africa’s Robert Misigaro:
For a first outing at a major tournament, Burundi can hold their head high as they showed an experienced Nigerian side they were ready for a showdown.
Burundi’s inexperience at this level of the game did not show in terms of discipline, approach to the game and composure, apart from a clear lack of finishers.
Even though they lost, Burundi have a lot to be proud of and can hope to do better against a lesser opponent. A 1-0 score against Nigeria in their first ever Africa Cup of Nations game is nothing to be ashamed of.
Meanwhile, Nigeria can expect anything but an easy ride in this tournament.