The veteran forward netted from the spot just after the hour mark to break the deadlock against Ghana in their first group game on Thursday evening.
Ronaldo, 37, was pictured fighting back tears during the Portuguese national anthem in his first game since having his contract terminated by the Red Devils.
Cristiano Ronaldo shrugged off his Manchester United exit with a World Cup goal for Portugal
The captain netted a controversial second-half penalty against Ghana at the Qatar tournament
The 37-year-old forward dived to the ground after minimal contact from Mohammed Salisu
But the confidently dispatched penalty, followed by his trademark ‘Siuuuu’ celebration, was highly controversial.
Ronaldo burst into the box and dived to the ground under minimal contact from Southampton defender Mohammed Salisu.
Referee Ismail Elfath – from America – awarded a spot-kick and VAR surprisingly did not overturn his decision.
Fans quickly rushed to social media to accuse the 37-year-old of an ‘absolutely pathetic’ dive and labelled him ‘trash’ for his actions in trying to fool the referee.
One said: ‘I just knew Ronaldo would dive. The game was becoming too tough for him to handle. It’s inevitable!’
A second added: ‘That Ronaldo dive was absolutely pathetic.’
Another fan posted: ‘That was the softest penalty call I’ve ever seen. What a dive by Ronaldo he’s trash.’