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 global goal to deny Portugal victory.
Mexico's Javier Hernandez, second from left, celebrates with teammates after scoring his side's first goal during the Confederations Cup, Group A soccer match between Portugal and Mexico, at the Kazan Arena, Russia, Sunday, .
Ronaldo, 32, is reportedly furious over a tax probe into the off-shore accounts dealing with his image rights, and has reportedly vowed to leave Spain.
The Euro 2016 winners kicked on again in the game's closing stages and Cedric netted with the help of a Hector Herrera deflection, but Moreno responded to earn a share of the spoils, with further talk of Ronaldo's uncertain club future sure to follow Portugal to their next match against Group A leaders Russian Federation.
The result left European champion Portugal and Gold Cup victor Mexico trailing host Russian Federation in Group A. Russian Federation opened the tournament with a 2-0 win over New Zealand on Saturday.
Forward Nani scored but a review by video assistants showed a Portugal player was offside in the build up to the goal.
Portugal defender Pepe thought he had opened the scoring in the 21st minute when he turned in a cross-shot after Ronaldo had smashed a shot against the crossbar, having blasted his initial free-kick into the defensive wall. Quaresma scores - Ronaldo bursts down the left after Salcedo fails to cut out a crossfield pass. Ronaldo loses the run of things as he brings the ball into the box, but turns out of trouble.
But the Portugal captain created another shooting opportunity for Quaresma with 10 minutes remaining and, although Ochoa saved comfortably, they continued to pile late pressure on Mexico.
But Mexico responded with Hernandez testing Portugal keeper Rui Patricio, before putting his side level.
Borussia Dortmund midfielder Raphael Guerreiro failed to deal with a cross into the box and Carlos Vela teed up Hernandez, who met the cross with a diving header. Poor defending, and a lovely goal.
After an explosive opening period, the second was a much tamer affair as both teams squandered half chances as the tempo dropped.
But with the 90 minutes up, Mexican defender Moreno rose highest from the final corner of the game to head in the equaliser.