Ahmed Musa scored twice on his return to the starting line-up as Nigeria kept their World Cup knockout hopes alive and dealt Iceland's chances a blow with a 2-0 win in Volgograd.
The Leicester forward, on loan at CSKA Moscow last season, struck a volleyed opener four minutes after the restart and further repaid boss Gernot Rohr's faith with a fine second 15 minutes from time.
Gylfi Sigurdsson looked set to give Iceland a late lifeline when Alfred Finnbogason earned a VAR-awarded penalty, but the Everton playmaker ballooned his 83rd-minute effort over the bar.
The result boosts beleaguered Argentina's hopes as well as the Super Eagles', but victory for Nigeria against Lionel Messi and co on Tuesday would see Rohr's side through alongside Croatia.
Iceland, who could still progress themselves but must win, started briskly as Sigurdsson saw a free-kick pushed away before curling straight at teenage goalkeeper Francis Uzoho from open play.
Nigeria were feeling their way into the contest as action in the stands - a Mexican wave soon followed by the booming Viking Thunderclap - caught the eye instead, but though Kelechi Iheanacho and Victor Moses were busy, they failed to muster a first-half shot.
Iceland were content to sit back against ineffective opponents but Aston Villa's Birkir Bjarnason had chances from a flurry of balls into the box, volleying over after a long throw and swiping through air when when Birkir Saevarsson drilled a dangerous diagonal across goal.
The game had been short on quality where it mattered but when the breakthrough came, it was in style. Moses was set free, ironically, by a familiar long Iceland throw but Musa stretched brilliantly to control his cross, before readjusting and lashing home.
Wilfred Ndidi's effort was well saved by goalkeeper Hannes Halldorsson as Iceland were rocked and Musa was soon in the mood again.
Moments after rattling the crossbar with a curling effort, he raced onto Leon Balogun's ball down the left, darting inside Kari Arnason and then rounding Halldorsson before tucking into an empty net.
Iceland were handed a way back when Tyronne Ebuehi was adjudged to have caught Finnbogason, referee Matthew Conger consulting with VAR before pointing to the spot, but though he had confidently clutched the ball in anticipation, Sigurdsson's aim was off.
Iheanacho fired wide for Nigeria in the closing stages and Finnbogason's angled drive was saved by Uzoho at the other end but time ran out for Iceland, their hopes of progress now in peril.
Man of the match - Ahmed Musa
Musa had to settle for coming off the bench in an opening defeat to Croatia but how he made his point here. Agility and quick feet were key to his first goal while pace and trickery delivered the second. With four goals, he is now his country's all-time top scorer in World Cup games; only Asamoah Gyan (six for Ghana) and Roger Milla (five for Cameroon) have scored more for an African nation.
Opta stats
- All six of Nigeria's wins at the World Cup have come against European opposition, and they have kept a clean sheet in five of those six victories.
- This was Iceland's first ever defeat in a group stage match at a major international tournament (Euros and World Cup), having previously drawn three and won one of four such games.
- This was only Nigeria's second win in their last 14 matches at the World Cup (D3 L9), having also beating Bosnia and Herzegovina in 2014.
- Nigeria did not attempt a single shot in the opening 45 minutes, the first side to do so in the first half of a World Cup match since South Korea against Algeria in 2014
- Iceland's Gylfi Sigurdsson fired in two shots on target in the first six minutes of this match, as many as his side managed in total in 90 minutes against Argentina in their opening match.
What's next?
Nigeria take on Argentina in a crunch St Petersburg clash at 7pm on Tuesday, while Iceland face already-through Croatia at the same time in Rostov-on-Don knowing only victory will do. Three sides remain in the hunt to qualify but goal difference could come into play.