When the captains are like blood brothers, and when they cuddle and kiss before the contest, it sends out (at best) mixed signals.
But Neymar Jr and Luis Suarez are only supposed to be so friendly when they play for Barcelona. In South America, where the eliminators are well under way towards the 2018 World Cup, they are on opposite sides.
Neymar is Brazil's leader, their inspiration.
Suarez is something else. He is, to use the word of one of his Uruguay team-mates, defender Jorge Fucile, a "demon".
A good and a bad demon, whichever way you look at it.
Friday's World Cup encounter in Recife, high up on Brazil's northern tropical coastline, was Suarez's comeback game. His nine-match Fifa ban for biting the shoulder of Italy's Giorgio Chiellini during the last World Cup had taken 20 months to serve.
And how exactly did Oscar Tabarez, the veteran coach of Uruguay, welcome back his demon? He made him captain, of course.
And, naturally, Suarez bit Brazil - legitimately.
Poor little Luis. All that fun, all those goals, all the trophies... and he felt deprived about not being allowed to play for his country. This is not meant to be beastly to Suarez. He is an extraordinary player who never gives up any ball as a lost cause.
It was Suarez, it had to be, who scored the final goal in a game where Uruguay came back from 0-2 down to end the night 2-2.
Brazil might dwarf Uruguay in size and population, but nobody who is old enough has ever forgotten what happened on July 16, 1950, when Uruguay pulled off a seismic shock by defeating Brazil 2-1 in the World Cup final in Rio de Janeiro.
There were 119,854 fans packed into the Maracana that day, and there were suicides reported as a consequence. Brazil, the best football nation on earth, have never before or since won a World Cup on home soil.
They have never failed to qualify for the tournament either, but there are those who fear that, while Dunga remains the coach, his presence could mean that they fail to qualify for the first time.
Dunga has always seemed out of kilter, too coarse, too physical and too negative a coach for his own country. But he remains in charge, and his post-game explanations remain familiar.
The Uruguayans, he said, are "always difficult" opponents.
"In the first half, we were rolling the ball and making the most of space. In the second, we were more static, without the movement. Uruguay took advantage," he said.
The way Suarez told it, Uruguay were shocked to concede a first-minute goal. "But like always," he then said, "this team showed rebellion and character."
It was their leader who showed those qualities. "Luis is our demon," Fucile repeated. "We all have respect for him. They didn't know how to mark him."
Actually, from the TV footage, it looked as if neither side knew how to mark the known scorers.
It took less than a minute - 42 seconds, to be precise - for Willian's cross to elude the entire Uruguayan rearguard and reach Bayern Munich winger Douglas Costa for him to poke home the opening goal.
After 26 minutes, Renato Augusto, these days plying his trade in China with Beijing Guoan, made it 2-0 by dummying the goalkeeper.
The biggest game of the weekend, with the arguable exception of Argentina coming from a goal down to beat Chile 2-1 in Santiago, was looking like a home banker for Brazil.
At this point, it is worth remembering that Lionel Messi is back for Argentina after a four-match absence through injury last autumn. And Messi, naturally, wears the armband for his country.
So that accounts for all three of them, the whole attacking trident for Barcelona, in leadership roles for their respective countries less than a week before they should be back in Spain for El Clasico against Real Madrid.
The threesome have just passed the century mark of games played together in Spain. Neymar has contributed 56 goals and 24 assists in his 79 appearances in that time, while Suarez has overtaken him with 68 goals and 39 assists from 86 matches.
And Messi? Well, he is playing deeper, by choice, seeking to be a more complete all-rounder, a playmaker as well as a member of the trident. So it's 86 goals and 33 assists in the 84 appearances Messi has contributed since the arrival of Suarez following the 2014 World Cup.
According to Suarez, he and his family have been through an emotional 20 months since Fifa banned him for his "mistake".
He needed to score on his Uruguay comeback because of the support of his family who know how much he has "suffered".
Poor little Luis. All that fun, all those goals, all the trophies and the acceptance at the Camp Nou, and he felt deprived about not being allowed to play for his country.
This is not meant to be beastly to Suarez. He is an extraordinary player who never gives up any ball as a lost cause, and an exemplary team player wherever he plays.
It was actually his fellow Uruguayan, the Paris St-Germain striker Edinson Cavani, who first found the weakness of Brazil at the back. That weakness, David Luiz, actually plays for the same PSG side as Cavani.
He knew how to beat him when, after 31 minutes, a back header reached Cavani who shot with a superb volley.
Luiz was the nearest defender to Cavani. Alas for him (chosen ahead of Thiago Silva and Marquinhos, both also of PSG), close was not close enough.
A similar thing happened just after half-time when Luiz allowed space for Suarez to hit the equaliser. His low shot went straight through the goalkeeper, and his celebration was to run to the touchline where he was handed a T-shirt.
It bore a tribute to the late Walter Ferreira, a physiotherapist who put off his own cancer treatment to get Suarez fit for the 2014 World Cup.
Before returning to Barcelona, Neymar serves a one-match ban and will miss Brazil's game in Paraguay on Tuesday. Suarez should play for Uruguay against Peru.
And Messi is expected to lead Argentina against Bolivia - on a pitch of rolled mud on which the Cordoba club allowed an Iron Maiden rock concert to churn up the grass.
Sometimes, they still do things differently in Latin America.
A version of this article appeared in the print edition of The Sunday Times on March 27, 2016, with the headline 'Uruguay still haunt World Cup dream of their age-old foes'. Print Edition | Subscribe
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