Substitute Cedric Soares looked like being the European champions' hero with his 86th-minute deflected shot, but Moreno's header from a corner spoiled the Southampton defender's celebration of his first worldwide goal.
Portugal did eventually take the lead on 34 minutes though, when Ronaldo broke through into the Mexico box and played a lovely pass to Ricardo Quaresma, who was completely unmarked on the right, and slotted past Guillermo Ochoa.
Ten minutes from time Portugal saw Quaresma's shot saved whilst at the other end Giovanni dos Santos failed to hit the target.
Fellow Confederations Cup Group A teams Russian Federation and New Zealand opened the tournament in St. Petersburg on Saturday, with the hosts running out comfortable 2-0 winners.
With Mexico still scrambling at the back, another delivery from the right was flicked into the bottom-left corner by Nani, but the referee - assisted by the VAR - disallowed the goal for offside.
Portugal ended 2-2 with Mexico and, perhaps fortunately for FIFA, Chile beat Cameroon 2-0.
More confusion was caused when Argentine referee Nestor Pitana called a review for unclear reasons after defender Cedric Soares's deflected shot in the 86th gave Portugal a 2-1 lead.
"I stand by Ronaldo's character and integrity, both as a man and as an athlete", said Santos, who coached Ronaldo when the player was a teenager in Portugal before leaving to play for Manchester United.
Ronaldo and his teammates can see the huge colorful depiction of the Portugal forward, but the public has no access to it. As the game continued to play out, however, Portugal showed why they are in fact one of the better countries in the sport, as they looked more and more risky on the counter.
"At the start we couldn't enjoy good control of the ball but then we managed to balance things out and could have won it". Despite the fact that the final whistle did not reveal the victor, having recorded in the asset of both teams on 1 point, Mexico still remains the leader of the group, reducing the gap from the nearest pursuer to 3 points.
'It's the new rule.
Mexico is in fine shape heading into the tournament attack-minded, possession-based style of football.