Goncalo Ramos grabbed a 94th-minute winner after Cristiano Ronaldo had scored his first goal in a World Cup knockout stage as Portugal came from behind to beat Croatia and progress to the last 16.
Second-half substitute Ramos rose above two Croatia defenders to head in from a superb Rafael Leao cross as a pulsating match looked to be heading for extra-time.
Josko Gvardiol thought he had rescued Croatia when he bundled home in the 13th minute of stoppage time, but the video assistant referee intervened and the goal was ruled out for offside.
Replays showed that Igor Matanovic got the slightest of touches on a cross that then fell to Mario Pasalic who was in an offside position before Gvardiol scored.
Portugal dominated the first half but it was Croatia who edged a frantic second period.
Ivan Perisic rifled a shot into the corner eight minutes into the second half after Ruben Dias could only half-clear a cross to the back post.
Half-time substitute Matanovic thought he had doubled Croatia’s lead two minutes later with a near-post finish, but the offside flag went up against team-mate Nikola Vlasic.
There followed a frantic few minutes during which Leao rattled the crossbar with a curling strike and Ronaldo saw a cute dinked finish ruled out for a marginal offside.
But just as it looked like he was about to be replaced, Ronaldo converted from the penalty spot after the video assistant referee spotted a foul on Renato Veiga at a corner.
Croatia responded well – and after the hydration break, Mateo Kovacic forced Diogo Costa into two quick-fire saves before Matanovic was foiled one-on-one.
Petar Sucic then ran on to a superb Kovacic through ball and finished coolly past Costa, but the offside flag went up once again.
Ronaldo was visibly unhappy to be replaced in the 81st minute, before Veiga and Mario Pasalic missed clear headed opportunities at either end.
Extra time seemed the fairest way to settle the contest before Ramos sparked wild celebrations.
In the last 16, Portugal will face European champions Spain at Dallas Stadium, Texas, on Monday, 6 July (20:00 BST).