Cristiano Ronaldo and Portugal were held to a surprise 1-1 draw by Congo in their opening match of the World Cup on Wednesday.

Congo, making its first World Cup appearance in 52 years, earned an impressive result against European opposition, becoming the second African team to make a strong start to the tournament after Cape Verde's goalless draw against Spain on Monday.

"The World Cup is a tournament where this happens," Portugal coach Roberto Martínez said. "At times the performance is not up to the challenge."

Playing before a crowd of 68,777 at NRG Stadium, largely made up of Portugal supporters, Congo secured the first World Cup point in its history after losing all three of its previous matches at the tournament.

Many Congolese supporters were unable to travel to the United States because of restrictions related to Ebola concerns.

"There was not enough blue in the stands, but the players are tough and they know how to overcome challenges," Congo coach Sébastien Desabre said. "I'm sure many Congolese people are proud of their team today."

Portugal took the lead in the sixth minute when João Neves headed home a cross from Pedro Neto.

However, Congo equalised deep into first-half stoppage time as Yoane Wissa headed in a cross from Arthur Masuaku, sparking celebrations among the Congo supporters present.

It was Congo's first-ever World Cup goal.

"It's crazy," Wissa said. "Fifty-two years later we are here, we are back. It's been long, it's been difficult. Scoring that goal means a lot for all Congolese people, for me, my family and the fans."

Congo's only previous World Cup appearance came in 1974, when the nation competed as Zaire and lost all three group-stage matches against Scotland, Yugoslavia and Brazil.

"The goal changed things," Martínez said. "We almost felt the fear of not losing the game."

Portugal struggled to find a winner despite several chances. Ronaldo missed opportunities in the 68th and 73rd minutes, sending both efforts wide of the right post.

Asked whether he considered substituting Ronaldo, Martínez dismissed the idea.

"It makes no sense to take off the world's top scorer when you need goals," he said. "Cristiano's experience in the box is important, and the way he attracts defenders is important."

Ronaldo became the oldest outfield player ever to start a World Cup match, surpassing the mark set by Canada's Atiba Hutchinson four years ago.

The Portuguese star also joined Lionel Messi as the only players to appear in six World Cups. Messi, who scored a hat trick for Argentina on Tuesday, and Ronaldo are now the only players to have played in six editions of the tournament. Ronaldo still has the opportunity to become the first player to score in six different World Cups.

Portugal came close again in the closing stages, but Bruno Fernandes sent a shot wide in the 90th minute.

João Cancelo thought he had restored Portugal's lead in the 55th minute with an acrobatic bicycle kick, but the goal was ruled out for offside.

At the other end, Cédric Bakambu nearly put Congo ahead, only to see his effort strike the near post.

Among those attending the match were the parents of Diogo Jota, the Portugal international who died alongside his brother in a car accident last summer. They watched the game from a luxury suite at the stadium.