Yoane Wissa’s header cancelled out Joao Neves’s early goal and the African side, appearing in their first World Cup since 1974 when it was known as Zaire, more than held their own.
Ronaldo, 41, was largely a peripheral figure throughout the match, failing to make the impact his great rival Lionel Messi had done on Tuesday in scoring a hat-trick against Algeria.
The DRC’s achievement was even greater given their preparations had been disrupted by the Ebola outbreak back in their country.
Some Portugal players were wearing wrist bands, given to them by their Prime Minister Luis Montenegro, in tribute to late team-mate Diogo Jota, who was killed in a car crash last year.
Portugal got off to the perfect start, with Neves powering home a header from Pedro Neto’s cross in the sixth minute.
However, despite dominating possession they lacked a cutting edge and well into time added on in the first half their opponents made them pay.
Wissa rose unmarked to head past Diogo Costa in the Portuguese goal sparking wild celebrations on the pitch, the bench and among the Congolese fans in the stadium as the Newcastle forward registered his country’s first ever goal at a World Cup.
Former Portuguese defensive bulwark Pepe, watching from the VIP seats, did not look impressed.
Bernardo Silva had started the day by joining Real Madrid on a free transfer but he ended it by watching from the bench after Martinez took him off at half-time.
He was briefly off his feet celebrating when Joao Cancelo’s overhead kick hit the back of the net, only for it to be ruled out for offside.
The Congolese were matching the Portuguese, though, and 35-year-old veteran striker Cedric Bakambu shrugged aside Bruno Fernandes, but his shot came back off the near post.
Ronaldo finally had a chance to shine when presented with a chance by Francisco Conceicao’s pass but he fluffed his lines sending it wide of the post.
The same combination linked up again minutes later, Conceicao – a far livelier presence than Silva had been – teeing up Ronaldo but once again the result was the same, the ball went wide.
Portugal thought they had at least got a corner but when it was not given Conceicao slammed the ball into the ground in frustration as his side failed to pick up three points in their opener. (AFP)