Iran kicked off their campaign with a 1-0 win against Morocco, thanks to a late own goal by Aziz Bouhaddouz, piling the pressure on Spain at Kazan Arena on Wednesday.
Morocco became the first team to get eliminated at this year's tournament following their 1-0 defeat to Portugal in Group m B on Wednesday.
Ronaldo's goal put the European champions top of Group B before Spain play Iran at 19:00 BST on Wednesday, and extended his lead as the top scorer in Russian Federation in the race for the Golden Boot.
"We are at a World Cup and we have to show Morocco respect because they are an excellent team". "Nothing is done in this group so we will have to be strong and determined".
Ronaldo, after his fearless header, also became the first Portugal player since José Torres in 1966 to score a goal with his right foot, left foot and head in a single World Cup. - Morocco have lost seven of their last nine World Cup matches (W1 D1), failing to score in over half of those games (5).
The Real Madrid star blitzed a hat-trick as Portuga and Spain played out a 3-3 draw on Friday.
"We're nearly there (knockout stages) and then we'll see". Morocco are giving a tough challenge to the Portuguese!
Morocco went on to lose the game 1-0, becoming the first team to be eliminated from the worldwide tournament.
However, Portugal held out and go on to complete their first-round against Iran while Morocco face Spain, both on June 25.
'I do not know what he (the referee) is used to, but he was very impressed by Cristiano Ronaldo, ' he told Dutch TV.
American official Mark Geiger is at the centre of the controversy with Morocco's coach, Herve Renard, also unhappy with a number of decisions made.
Ronaldo's success has come at an event in which he has previously struggled to be at his best, and he has eclipsed his goal tally from his combined 13 appearances at his three previous World Cups.