However the goal was ruled out after the three Video Assistant Referees reviewed it and found out a Portuguese player was in an offside position.
Both Confederation Cup games played on Sunday in Russian Federation left teams confused by decisions - reached more slowly than expected - by referees taking advice from assistants watching multiple replays.
"It wasn't the result that we wanted", said Ronaldo.
He also scored important goals in the decisive stages of the Spanish league, a competition Madrid won this season for the first time in five years.
The result puts the sides level on one point each in Group A, behind hosts Russian Federation, who defeated New Zealand 2-0 in their opening game clash in St. Petersburg on Saturday.
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Summer is finally here and you know it because of those wonderful double-digit million dollar Mondays. Maybe he and Wonder Woman can recreate the iconic scene at the pottery wheel from the movie Ghost .
"If this is going to happen several times during a game, well it's not very pleasant for the players", Cameroon coach Hugo Broos said.
The score was 1-1 at half-time, as Javier Hernandez responded from close range after Ricardo Quaresma had opened the scoring, but the highlight of the first half was the pass from Cristiano Ronaldo that set his long-time global teammate up.
Southampton defender Cedric Soares looked to have won it for Portugal as his shot towards goal looped off a defender and in for 2-1 in the 86th minute. "We faced the European champions, a team that plays at a very high level, and we played equal to them".
As it stands, Russian Federation sits at the top of the group, followed by Portugal and Mexico while New Zealand, who were thumped by the hosts 2-0 on Saturday, are bottom.
Mexico's all-time top scorer grabbed his 48th worldwide goal from 93 appearances after some awful defending by Portugal.
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With that, the result now gives both of the teams one point, a fair result. "It is an aggressive team, pressing you all the time, but I think that we have enough quality to win this game".
Ronaldo made a great run from near midfield to set up Quaresma's 34th-minute goal. Santos's side improved from there, though, and when Carlos Salcedo allowed Ronaldo in on goal on the left, the forward quickly adjusted to an uncharacteristic stumble to slip a pass into the box for Quaresma, who coolly rounded Guillermo Ochoa to prod into the net.
However, Mexico secured a point in stoppage time when defender Hector Moreno rose well to head home from close range.
Another defensive error led to Mexico's equaliser just before the break as Raphael Guerreiro lost sight of Raul Jiminez's cross and Carlos Vela popped the ball back across for Hernandez to head in. I said we were not the favourites, but that we were candidates to win it.
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But his 9-foot putt to save par edged just short of the hole, and he had to tap in for bogey. Thomas capped his sensational round with an eagle after landing a 3-wood on the 18th green.
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