Cristiano Ronaldo will aim to put his painful Manchester United divorce behind him at the World Cup on Thursday as Brazil also make their bow following a win for Switzerland in the early kick-off.
Ronaldo's preparations for what is likely to be his last World Cup have been overshadowed by his sudden departure from Old Trafford this week after he lambasted the club in a TV interview.
The Portugal superstar's form this season has been poor but he is still hoping for a final shot at glory in Qatar after leading his team to the Euro 2016 title.
In Pics | Youngest players to score in the World Cup
The 37-year-old, whose club future is uncertain, is aiming to become the first player in history to score at five World Cups.
Portugal coach Fernando Santos said his men were entirely focused on their opening Group H match against Ghana despite the distractions of the media circus surrounding their captain.
"The players are absolutely focused, with a great spirit, convinced about what they have to do, what their objectives are and realistic about the challenges they are facing," he said.
"Winning a competition of this magnitude is difficult."
World Cup favourites Brazil launch their bid for a record-extending sixth global crown against a dangerous Serbia side.
Also Read | FIFA World Cup: How opening game losses affect qualification chances
Brazil boast a frightening array of attacking talent including Paris Saint-German forward Neymar and Real Madrid pair Vinicius Junior and Rodrygo.
Coach Tite will be wary of his Group G opponents after witnessing shock defeats for Argentina and Germany already in Qatar.
"In my opinion these players (attackers) will help Neymar because they can divide up the responsibility and create space for him," said veteran Brazil skipper Thiago Silva.
"The atmosphere in the squad is super-healthy," he added. "The mixture of young players and more experienced ones creates a great connection."
Serbia appear a more dangerous proposition than four years ago, when they also faced Brazil in the group stage but lost 2-0 and exited in the first round.
"We are afraid of nobody in the world, not even Brazil," said Serbia coach Dragan Stojkovic, who hopes prolific Fulham striker Aleksandar Mitrovic will be fit for the match at the Lusail Stadium.
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 their eighth straight loss at World Cups -- a miserable run stretching all the way back to 2002.
Son Heung-min was named in the starting line-up for South Korea's Group H opener against Uruguay at 1300 GMT even though he was wearing a mask after suffering a fracture around his left eye earlier this month.
Uruguay coach Diego Alonso selected Luis Suarez up front, with fellow veteran Edinson Cavani on the bench.
Germany coach Hansi Flick said no member of his team was safe after their shock 2-1 defeat against Japan on Wednesday.
The four-time champions, who next face Spain, are facing a nightmare scenario of a second consecutive group-stage exit after their early departure in Russia in 2018.
"You can understand that we are discussing every matter of personnel and every position," Flick said.