A revamped but businesslike Croatia has topped its World Cup Group D as Ivan Perisic's last-gasp goal helped it maintain its flawless record with a 2-1 win that also ended Iceland's qualification hopes.
Shortly after half-time though, Milan Badelj put Croatia in front with a textbook half-volley from Perisic's cross. A Nigeria draw or loss opens the door for Iceland, which must win and win any potential tiebreaker with Nigeria (in the event of a draw in the other Group D match) or Argentina (in the event of a win over Nigeria).
Everton's Sigurdsson tested Lovre Kalinic from a free-kick, while Birkir Bjarnason, who suffered a nosebleed early on, had shots blocked in quick succession.
Iceland made three changes from their defeat to Nigeria, with Johann Gudmundsson the most notable change back in midfield, replacing Rurik Gislason.
Croatia improved from a display which had failed to register a convincing effort in the first half, with Badelj striking the bar before going one better a minute later, half-volleying into the ground and beyond Halldorsson from eight yards.
Sverrir Ingason forced Kalinic to another spectacular save, seconds before his header shaved the top of the bar.
Instagram launches hour-long videos as it celebrates one billion users
With minimal navigation, users can swipe between the sections "For You", "Following", "Popular" and "Continue Watching". Users will have access to comments, related content and other features taken from Instagram on IGTV .
Though they appeared deflated in the ensuing minutes, Sigurdsson was rewarded in the 75th minute with referee Antonio Mateu awarding Iceland a penalty for a handball on substitute Dejan Lovren. Luka Modric and company secured a 2-1 win over the first-time participants.
But as Iceland strained for the victor and a berth in the last 16 it was Croatia who threatened, free-kicks by Perisic and Rakitic worrying Halldorsson.
Croatia have won three consecutive World Cup matches for the first time.
Croatia midfielder Mateo Kovacic completed 78 of his 79 passes attempted in this game (98.7%); the best percentage of any player to start the match.
Croatia lost 1-0 to Iceland in a World Cup qualifier and had to go through the playoffs to reach the finals so they will be taking nothing for granted despite speculation that coach Zlatko Dalic could field a second-string team.