Ronaldo struck in the 33rd minute, his 75th goal for his country, and Bernardo Silva put the European champions in the driving seat with the second four minutes later. Portugal would add two more goals in the second half, with Andre Silva scoring in the 80th minute and Nani doing so in the first minute of second-half stoppage time.
Mexico eliminated hosts Russian Federation with a 2-1 win to join Portugal on seven points, with the Gold Cup winners to meet the second-placed side from Group B in the last four.
Alexander Samedov had given the Russians the lead on 25 minutes, only for Nestor Araujo to fire the Mexicans level five minutes later.
According to organizers, a total of over 41,500 people attended tonight's match at Kazan Arena.
The win, however, came at a cost as Manchester City-bound midfielder Bernardo Silva was substituted because of an ankle injury.
Portugal have progressed through to the semi-finals of the Confederations Cup with a 4-0 win over New Zealand.
Juan Carlos Osorio's side finished in second position with seven points behind Portugal (due to an inferior goal difference of +2) who also defeated New Zealand 3-0 to set up a semi-final clash with the victor of Group A.
Severe storm warning issued for SW Crawford County
Some isolated showers will stick around for the morning commute Monday along with areas of patchy haze and fog. This is shown in the graphic below, with a almost two-inch bull's eye over the greater D.C. -Baltimore region.
"We knew it could be complicated because we had seen New Zealand play Mexico and the problems they caused the Mexicans".
But Portugal did eventually come to life and Ronaldo forced Marinovic into a straightforward save with a header from a right-wing delivery after 24 minutes.
And Mexico went on to take the lead in even more weird circumstances early in the second half, with Akinfeev completely misjudging a long ball and presenting Hirving Lozano with a simple headed finish.
Marinovic made impressive saves to deny Ronaldo, Andre Silva and Nani, but was powerless to stop Andre Silva or Nani late in the game.
Russia's early exit from the tournament was another setback to next year's World Cup hosts who also failed to surpass the Euro Cup group stage as they went home without winning a game. The defender headed the ball into the opposite corner, over Akinfeev.
Mexico had a second-half goal by defender Hector Moreno disallowed for offside after video review.
"Given we've only played six, seven, eight games against these [top] teams in the last three years we've got so much to look forward to and so much potential in us".
Akinfeev should've dealt with it, but indecision between him and defender Viktor Vasin allowed Lozano to bravely steal in and steer the ball in for Mexico's victor seven minutes after half-time.
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