Ronaldo became the first man to score in five different editions of the World Cup as he slotted home a controversial penalty to help Portugal down Ghana 3-2 in their Group H clash.

The typically ice-cold spot-kick was Ronaldo's eighth career goal at the World Cup and comes after a tumultuous week that saw the star forward make a sensational exit from Manchester United after weeks of tensions with the club.

"It was a beautiful moment, my fifth World Cup, we won, and we started with our good foot," Ronaldo said after the win.

"It's a very important win, we know the first match is crucial, but the world record is also something that makes me very proud."

But there was controversy surrounding the penalty, which was awarded after Ronaldo crashed theatrically to the turf following minimal contact with Ghana defender Mohammed Salisu.

Furious Ghana coach Otto Addo described the penalty decision as a "gift" to Ronaldo.

"I think it was a really wrong decision, we were playing the ball [...] I don't know why VAR didn't come up, there is no explanation," Addo said.

"If somebody scores a goal then congrats, but it was really a gift [...] a special gift from the referee."

In Thursday's late game, Brazil was rocked by an injury scare involving captain Neymar after two goals from Richarlison secured a 2-0 win over Serbia in Group G.

Paris Saint-Germain superstar Neymar was substituted with 11 minutes remaining and was later seen with a badly swollen right ankle as he left the field.

It was the latest in a series of injury dramas surrounding the Brazilian talisman, whose 2014 World Cup was ended by a back injury.

The Brazilian skipper was also ruled out of the 2019 Copa America due to torn ligaments in the same right ankle. He also missed 10 weeks of the 2021/2022 season with an injured left ankle.

Brazilian team doctor Rodrigo Lasmar said after the win it was too early to give a clear prognosis on his latest knock.

"We need to wait 24 to 48 hours to have a better assessment," Lasmar said. "We need to wait, we cannot make any premature comments about his evolution."

Brazil coach Tite however said he was confident Neymar would be fit for the remainder of the tournament.

"You can be certain that Neymar is going to play in the World Cup," Tite told reporters.

The injury took the shine off a Brazilian win that came through goals from Tottenham's Richarlison, including a spectacular volleyed second goal.

"It's a childhood dream come true," Richarlison said afterwards. 

"We played a good game, especially in the second half, when the opponent got tired, and we managed to take advantage of that."

Switzerland and Cameroon, also in Brazil's group, kicked off Thursday's action in Qatar, with the Swiss winning 1-0 courtesy of a goal from Cameroon-born Breel Embolo.

The forward struck three minutes into the second half at Al Janoub Stadium as Switzerland secured a vital three points.

Granit Xhaka and Remo Freuler worked the ball out wide on the right to Xherdan Shaqiri, whose low cross into the area was swept home by an unmarked Embolo, who chose not to celebrate against his birth country.

"It's quite special for him because of his links to Cameroon -- I'm very happy he's playing for us," said Swiss goalkeeper Yann Sommer. "He's always right there when you need him."

Defeat condemned Cameroon to its eighth straight loss at World Cups—a miserable run stretching all the way back to 2002.

In Thursday's other game, the return of Tottenham star Son Heung-min was not enough to inspire South Korea to victory with the Asian side grinding out a 0-0 draw with Uruguay in Group H.

The striker wore a mask to protect the injury he suffered while playing in the Champions League for Spurs as South Korea took a point in their opener.

The 30-year-old had surgery for fractures around his left eye just three weeks ago and this was his first time playing competitively since.

"I feel ok, I'm not the only one to wear a mask, some players wear masks. I feel comfortable," he told reporters afterwards.

"I'm just happy to be here, happy with the mask that I could play, it's just so amazing."

Meanwhile, the shockwaves from Germany's monumental upset defeat to Japan on Wednesday continued to reverberate, with coach Hansi Flick warning no member of his team was safe after the 2-1 loss.

The four-time champion, which next faces Spain, is facing a nightmare scenario of a second consecutive group-stage exit after its early departure in Russia in 2018.

"You can understand that we are discussing every matter of personnel and every position," Flick said.