In a split second, Ronaldo had gone from savoring a last-gasp winner for his country to protesting what he considered a refereeing oversight with no video review available.
The Portugal star came oh-so-close to scoring a stoppage-time goal when Serbia defender Stefan Mitrovic slid and swept the ball to apparent safety.
For Ronaldo, the ball had completely crossed the line. For Dutch referee Danny Makkelie it had not, and he rewarded Ronaldo's complaints with a yellow card.
The incident will no doubt be used by fans of video review to argue for VAR in qualifying matches for the world's most important soccer tournament.
For 10-man Serbia, it was the perfect ending to an inspired fightback from a two-goal deficit.
For Diogo Jota, Portugal should have done more with the two goals he scored in the first half.
"It looked like the hard part was done, but then they changed the system in the second half, scored quickly, and built on from there," Jota said. "At 15 minutes into the second half, we have already let Serbia draw. We had to kill the game."
Serbia and Portugal were left with four points each atop Europe's Group A.
Luxembourg is next with three points after it stunned Ireland with a 1-0 victory in Dublin. That left Ireland and Azerbaijan with zero points.
Portugal looked ready to roll to a convincing win after Jota scored two headers.
The Liverpool forward got Portugal going in the 11th with a run to the left post where Bernardo Silva found him with a perfectly placed cross. Ronaldo helped by drawing in three Serbia defenders before laying off for the unmarked Silva on the right side of the box.
Serbia tried to respond through the runs by left back Filip Kostic and the playmaking of midfielder Dusan Tadic. But the hosts never seriously threatened Anthony Lopes' net before Jota made it 2-0.
This time it was for right back Cédric to send a cross to the heart of the box where Jota separated from Nikola Milenkovic and sliced a glancing header off the post and into the net in the 36th.
The double gave Jota five goals in 11 international appearances.
But Serbia got back into the match after coach Dragan Stojkovic made two changes at halftime.
Substitute Nemanja Radonjic needed less than a minute to pass for Aleksandar Mitrovic to head home and set a Serbia national team record with his 39th international goal.
On Wednesday, Mitrovic came off the bench to score a pair of second-half goals to rally Serbia for a 3-2 win over Ireland.
Serbia pressed for an equalizer, and Lopes had to stretch to palm Tadic's strike over his bar in the 54th.
But Lopes was beaten in the 60th when Serbia mounted a counterattack, with the ball flowing forward from Tadic to Radonjic, who played Filip Kostic clear to slot the ball home.
Ronaldo was denied his chance to play the hero shortly after Serbia defender Nikola Milenkovic saw a direct red card for a dangerous studs-first tackle of Danilo.
