Ghana's two goals against Portugal made them the first African qualifying team in this year's tournament to score.

Group G leaders are emerging in predictable form with Brazil ahead, Switzerland are second in the group after they beat Cameroon 1-0 and Serbia are bottom.

Group G

Breel Embolo's goal has lifted Switzerland to a 1-0 win over Cameroon at the World Cup and he kept his promise not to celebrate scoring against the country where he was born.

The Swiss forward from Yaounde struck with a right-foot shot in the 48th minute of Thursday's match, standing all alone eight metres out in the middle of the goalmouth to take Xherdan Shaqiri's low pass.

Embolo then pursed his lips in a wry smile and held his arms out wide, before raising his hands in a gesture of apology as teammates rushed to him near the penalty spot.

He pointed toward Swiss fans behind the goal where he had scored, then to Cameroon fans at the opposite corner of Al Janoub stadium.

The 25-year-old forward left Cameroon with his family when he was five. They spent time in France before settling in Switzerland, the country he is now representing at a second World Cup.

Group H

Uruguay faltered in their World Cup opener against a lively and energetic South Korea as they were held to the fourth 0-0 draw of the World Cup.

Both teams struggled to find the clinical edge despite plenty of attacking quality on show in their in Group H clash on Thursday.

Clear-cut chances were rare for either side at the Education City Stadium and although Uruguay created more opportunities, neither team managed a shot on target.

Uruguay captain Diego Godin and midfielder Federico Valverde were denied by the woodwork while South Korea forward Hwang Ui-jo blasted over the bar with the goal at his mercy, leaving both teams to rue missed chances

There were only a few hundred South Korean supporters in attendance but they were chanting throughout the contest, the beat of their drums matching the fast and frenetic pace of play.

"We're a very brave team, we're not afraid of our opponents," South Korea coach Paulo Bento said.

Group H

Ghana coach Otto Addo has complained about the officiating in his side's 3-2 defeat by Portugal in the World Cup, saying Cristiano Ronaldo's history-making goal was a gift from the referee.

Ronaldo won, and then converted, a 65th-minute penalty to hand Portugal the lead and become the first man to score at five World Cups as they went on to win their Group H game.

However, Addo felt American referee Ismail Elfath had made the wrong call.

"I think it was a really wrong decision, we were playing the ball ... I don't know why VAR did not come up, there was no explanation for it," said Addo about the soft penalty award after Ronaldo went down following minimal shoulder-to-shoulder contact with Mohammed Salisu.

Asked about Ronaldo's milestone goal, Addo said: "If somebody scores a goal, congratulations. But this was a gift, really a gift."

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Group G

Brazil striker Richarlison scored twice including a spectacular swivelling volley to get his nation's quest for a sixth World Cup title off to a perfect start in a 2-0 win over Serbia.

The Tottenham Hotspur forward has been in fine form when wearing the golden yellow kit of Brazil this year and opened the scoring with an easy tap-in before doubling the lead with his acrobatic effort.

Tite's decision to go with four forwards - Neymar, Vinicius Jr., Raphinha and Richarlison - in his attacking lineup paid off handsomely as the South Americans dominated the match and made Serbia work hard every time they went forward.

Vinicius used his acceleration to good effect to constantly beat his man while Neymar, playing in a free role, often found pockets of space, but a well-drilled Serbian defence kept Brazil at bay in the first half.

Serbia had been sweating over the fitness of their all-time top scorer Aleksandar Mitrovic but coach Dragan Stojkovic named him in the starting team.

- with Australian Associated Press