The Nassr captain, 38, struck the opener on Sunday night in his side’s 3-1 victory against defending champions Raja Casablanca at the Prince Sultan bin Abdulaziz Stadium in Abha.
Sultan Al Ghannam and summer recruit Seko Fofana put Nassr 3-0 up – it marked the Ivory Coast international’s first goal for the club – before Abdullah Madu’s own goal minutes from half-time gave Raja some hope.
However, the win sent Nassr into the last four, where they will meet Al Shorta on Wednesday after the Iraq club saw off Al Sadd of Qatar 4-2 on Saturday.
Posting on social media following his third goal in three games, Ronaldo said: “Into the semi-finals. Great feeling to keep scoring and helping the team to move forward in the competition!”
Runners-up in last season’s Saudi Pro League, Nassr are attempting to win the tournament for the first time. On Sunday, they gave a first start to Sadio Mane following last week’s move from Bayern Munich.
In the day's other quarter-final, UAE side Al Wahda lost out on penalties to Riyadh’s Al Shabab after the match in Taif had finished goalless.
Shabab had defender Iago Santos sent off just before the half hour, while opposing right-back Abdullah Al Karbi saw red for Wahda on 67 minutes.
In the shootout, Fares Juma was the only player not to convert, meaning Shabab advance to the semi-finals against Riyadh rivals Al Hilal. That match also takes place on Wednesday.