The Newcastle striker put aside the frustration of his injury-hit first season with the Premier League club as he headed home to secure a 1-1 draw under a closed roof at Houston's NRG Stadium on Wednesday.
Joao Neves had put Portugal, one of the pre-tournament favourites, ahead after just six minutes but they were unable to build on their strong start as DR Congo – making their first World Cup appearance in 52 years – fought back in the group K opener.
Ronaldo, matching Lionel Messi's feat of appearing at a sixth World Cup, didn't have the same sort of sensational impact that his old Argentine rival had enjoyed the previous night with his hat-trick against Algeria, as 'CR7' failed to convert two difficult late chances after a quiet game.
DR Congo deserved their point for a disciplined display after overcoming a difficult start.
The African side sat deep early on and were punished as Portugal controlled possession and soon created the opening goal.
It came from a move down the left as Pedro Neto found space and whipped in a cross for Neves to rise and power a header into the top corner.
The Leopards responded by adopting a more attacking approach with Wissa lashing a shot wide and Cedric Bakambu also threatening.
On the day it was announced he had signed for Real Madrid, Portugal's Bernardo Silva was booked for a poor challenge on Edo Kayembe as DR Congo continued to grow into the contest.
Portugal had another good spell but Bruno Fernandes drove a cross through the box and both Neto and Joao Cancelo failed to pick out Ronaldo.
DR Congo finished the first half strongly and drew level in stoppage time.
A short corner was worked to Arthur Masuaku and he swung a ball into the box for Wissa to arrive unmarked at the back post and head past Costa.
Portugal thought they had reclaimed the lead 10 minutes into the second half after a brilliant overhead kick from Cancelo but the former Manchester City defender was offside.
DR Congo also went close at the other end when Bakambu stole the ball from Fernandes and smashed a shot against a post, but the referee had already blown for a foul.
Portugal looked to Ronaldo for inspiration but he twice missed the target from Francisco Conceicao cutbacks. Cancelo also drilled in a ball looking for Ronaldo but it was too close to Lionel Mpasi.
DR Congo were increasingly forced back but did go close again on the break when Bakambu shot wide as they held on for a surprise point.
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