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MOSCOW -- Men's football is a game of fathers and sons, biological and adopted, real and imagined. Monday night's game between Iran and Portugal is a loser-loses-it-all clash for the right to advance to the last 16.

Portugal advance with a win or draw, Iran with a win.

Iran versus Portugal features a rather bad-blood, personal contest between Ronaldo and the man who stands in his way of greatness, Carlos Queiroz, both seen here at Manchester United in happier times. Getty

But the high-stakes match in Saransk also pits two compatriots against each other who were once so close that Team Melli coach Carlos Queiroz was referred to as Cristiano Ronaldo's "dad" by his then Manchester United teammate Ruud van Nistelrooy. For one game, they are united only in their grim determination to deny each other historic greatness.

Queiroz's energetic, tactically astute side are the latest obstacle four-time-scorer Ronaldo needs to overcome in the improbable, if not impossible quest to impose his genius on the World Cup and take an otherwise unremarkable team to their greatest glory.

Iran's dreams are more modest but no less heartfelt. Qualification for the second round would be a widely hailed first and undoubtedly trigger more mixed-sex street celebrations that the government frowns upon but will be powerless to stop. TV footage from female Iranian fans in Russian stadiums have opened the floodgates back in Tehran, as women fought off an official prohibition to watch live footage of the narrow, unlucky 1-0 defeat against Spain in Kazan.

Going into his second World Cup with the Islamic Republic, Mozambique-born Queiroz was being feted as "Mr. Football Nation" and "The Father of Success."

"In my seven-year career [in Iran], the Portugal match is the most interesting and important match for me," Queiroz said ahead of travelling to Saransk. To increase his sky-high popularity levels even further, he must defeat the individual might of a friend turned foe.

Queiroz used to manage Sporting in the mid-'90s before taking on a role as Alex Ferguson's assistant and advising him to buy a prodigious, 18-year-old winger. Cristiano Ronaldo's transfer to Old Trafford was brokered in Queiroz's apartment in Lisbon.

"I felt it was my duty as a friend and coach, and [I] do not regret it," the 65-year-old said after the 2014 World Cup.

In Guillem Balague's "Ronaldo" biography, Queiroz explains how he helped the young talent to fulfill his potential by pushing him to be more of a goal scorer and to simplify his game. Their relationship was so strong at United that Van Nistelrooy, who fell out with the winger over his habit of holding on to the ball too long on the wing, flippantly told Ronaldo to talk to his "dad" Queiroz in a training argument in May 2006.

The Portuguese forward took that remark particularly badly, having lost his father to liver cirrhosis eight months earlier. Van Nistelrooy had picked a fight he couldn't win. The Dutchman was shipped out to Real Madrid soon after.

When Queiroz took over Portugal as national coach in 2008, he immediately named Ronaldo and lavished him with public praise.

"Cristiano is a champion, and as a player, he is Superman," Queiroz said. "In terms of his mental approach to the game, he is so strong and so confident."

But Queiroz's defensive set-up and lack of emotional connection with the squad proved kryptonite for the national team's results and his friendship with the nation's star player. Ronaldo scored a single goal in 16 months of laboured performances. Following the country's elimination at the hands of Iberian rivals Spain at the last-16 stage in South Africa, Ronaldo answered a question about the reasons for defeat with a curt, "Ask Queiroz."

"We didn't speak after that," the manager said. "I would be a hypocrite if I said that I liked his comments."

Ronaldo was not called up to the national team again until Queiroz was fired in September 2010. According to Portuguese sources, mutual resentment still lingers. In an interview with FIFA.com in February, Queiroz spoke of "memories of shared projects" but pointedly refused to offer any olive branch to his former player.

There's a small possibility this intra-Portuguese duel could end with both men and their teams going through -- if Portugal lose and Spain were to lose by a bigger margin against Morocco -- but it's much more likely that football will borrow a compelling storyline from another genre on Monday night: that of an intensely personal battle between the master and his erstwhile apprentice.