Ramos connected with a superb pass from Rafael Leao in the fourth minute of stoppage time to snuff out a Croatia team which had created the lion’s share of the chances in sapping evening heat in Toronto.
In a dramatic ending, Croatia thought they had equalised in the dying seconds but Josko Gvardiol’s goal was chalked off for offside.
Cristiano Ronaldo played his role in the victory, stroking home a penalty that cancelled out Ivan Perisic’s opener.
It was Ronaldo’s first ever goal in the knockout phase of the World Cup and his remarkable international career will have another chapter when Portugal face Spain in Dallas on Monday.
Perisic had stunned the Portuguese by slotting the ball under the advancing Portugal goalkeeper Diogo Costa in the 53rd minute.
Within minutes, Ronaldo had the ball in the net after controlling a long pass, but his effort was disallowed for offside.
But Portugal got level when Renato Veiga was grabbed by Croatia’s Nikola Vlasic in the penalty area and after a VAR check, the referee pointed to the spot.
Ronaldo stepped up to convert the penalty with ease, hitting the ball straight down the middle of the goal and pumping his fists with joy afterwards.
In a pulsating game, Manchester City forward Mateo Kovacic’s low shot was pushed onto a post by ‘keeper Costa’s fingertips.
Still Croatia pushed and Peta Sucic had the ball in the net but the assistant referee’s flag was up for a clear offside.
Ronaldo was withdrawn in the 81st minute to allow Ruben Neves to come on.
Croatia continued to create more chances than their opponents and Mario Pasalic came so close to winning the game with a header at the far post, but it bounced just wide.
But when Ramos connected, the net bulged and Portugal were through.
