Switzerland's Breel Embolo scored the only goal against Cameroon - the country of his birth - in a hard-fought World Cup Group G opener.
Embolo refused to celebrate when he finished off a slick Swiss attack shortly after half-time.
The Indomitable Lions were unfortunate to lose after an enterprising display at the Al Janoub Stadium in Qatar.
Victory was vital for Switzerland, as both sides still have to face Brazil in the group.
Embolo moved to Switzerland from Cameroon with his family as a six-year-old and pledged his allegiance to the European nation after being granted citizenship in 2014.
At the age of 18, he set up the Embolo Foundation to support refugee children in Switzerland and disadvantaged children in the country of his birth.
He said before the game it would be "a very special" occasion to play against Cameroon and when he scored, he respectfully raised his arms and closed his eyes.
"I told him, 'Breel, friendship until the start, then they are your opponents,'" said Switzerland coach Murat Yakin. "Football writes such stories but he completed his mission.
"I am very happy with his performance."
Cameroon boss Rigobert Song admitted afterwards he would "have liked him to be on my side" but did say he was "proud" of Embolo.
"We are all proud of our country and you saw he did not celebrate the goal," said Song. "That is part and parcel of football and I'm proud of him."
Embolo's strike ensured victory for a side with high expectations - Yakin has declared his squad "the best Switzerland side ever" and said he expects them to achieve their best return at a World Cup.
After the game, captain Granit Xhaka echoed his coach's comments, arguing "we can beat anyone" and pointing to their record in recent tournaments as evidence of their potential.
Yet Switzerland struggled in the first half in the face of a vibrant Cameroon start and ought to have gone behind, with Eric Choupo-Moting, Bryan Mbeumo and Martin Hongla all missing presentable opportunities.
The goal rocked Cameroon and the Swiss had chances to extend their lead, only for Andre Onana to save superbly from Ruben Vargas, while Embolo and substitute Haris Seferovic were denied by last-ditch defending.
The Indomitable Lions have now lost eight successive games at the World Cup finals but Song's side impressed at times here.
Song admitted afterwards their next game against Serbia will be "decisive" if they are to stand any chance of becoming the first Cameroon team to progress beyond the group stage since 1990.
For Switzerland, the win gives them breathing space before their match against group favourites Brazil on Monday.
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