But he was unable to get the better of Sweden goalkeeper Andreas Linde, who seemed well prepared for him.
Nigeria eventually found the opener six minutes from time, when Stanley Amuzie delivered a pinpoint, curling cross in open play from the left wing which found Umar.
The AS Roma player made no mistake, scoring with a diving header for the African under-23 champions.
They continued their dominance in the second half, with captain Mikel Obi firing a well-driven shot from the top of the area, which was well saved by Linde.
The Swedish goalkeeper had to be alert four minutes later when Etebo dribbled inside the corner of the penalty box and attempted a curling effort, but Linde once again saved.
Coach Hakan Ericson used all three of his substitutes — Ken Sema, Muamer Tankovic and Jacob Une Larsson – to try and give his team a new dimension.
But, in the end, Nigeria’s backline was up to the challenge and held on for all three points thereby qualifying for the quarter finals of the competition.
On Wednesday, Nigeria will close out group play against Colombia in Sao Paulo.
Sweden meanwhile have a must-win match ahead against Japan in Salvador if they are going to continue their Rio 2016 journey.