A stunning fourth-minute save from Dominik Livaković ensured Bruno Fernandes couldn’t give Portugal the lead at the end of a lightning-quick break.
Croatia were under pressure for virtually the entire opening 10 minutes thanks to wave after wave of Portuguese attacks, with Ante Budimir’s off-target header all that the Vatreni could manage in response.
Cristiano Ronaldo could only hit the wall with a direct free-kick, whilst Renato Veiga completely missed the target with a powerful free header.
Despite Portugal having two-thirds of possession and seven attempts at goal by the first hydration break, the game remained goalless.
A wicked ball into the box saw both Fernandes and Ronaldo come within a whisker of opening the scoring, and aside from the occasional break upfield by the Croatians, the pattern of play continued until the half-time whistle.
The only surprise was that the teams remained on level terms at the interval, with Rafael Leao’s skied effort in stoppage time rather summing up the first half from a Portuguese point of view.
Nuno Mendes almost broke the deadlock in the opening minute of the second half after a strong and purposeful run, before some long-overdue Croatian pressure saw Ivan Perisic, left all alone at the far post, drill home the opener past Diogo Costa.
In so doing, he became the highest-scoring Croatian player in World Cup history, surpassing Davor Suker.
Costa denied Petar Sucic, before the offside flag saved Portugal from conceding a second, Leao’s stunning shot against the bar almost brought an equaliser, and Ronaldo also saw an effort ruled out for a marginal offside in a remarkable period of play.
Four Portuguese subs on the hour was an incredible roll of the dice from Roberto Martinez, and shortly after, Veiga being hauled down in the area by Nikola Vlasic gave Ronaldo the chance to score from the penalty spot, a chance he took with aplomb, hitting the shot straight down the middle to wrong foot Livakovic.
Mateo Kovacic saw his powerful effort hit the post as Croatia threatened again, and with 10 to play, Sucic had a goal chalked off. Ronaldo’s substitution soon after was met with a chorus of boos, and only Mario Pasalic will know how he missed the target with a minute left of normal time.
During the 10 minutes of stoppage time, Goncalo Ramos rose highest to glance Leao’s cross home and edge Portugal ahead for the first time.
Having played 113 minutes, Josko Gvardiol looked to have sensationally sent the game to extra time, but another offside decision gave Portugal the reprieve and secured the trip to Dallas to take on their Iberian rivals on Monday.
The result means that Portugal have still never lost a competitive game against the Vatreni (W6, D1), and have only lost one of the 11 H2Hs overall (W8, D2).
Flashscore Man of the Match: Ruben Dias (Portugal)