It will be an emotional farewell at Jose Alvalade Stadium when Ruben Amorim takes charge of his final home game as manager of Sporting. He will wave goodbye to the fans but it also marks the end of a partnership that has changed the face of Portuguese football in the last four years.

Working quietly in the background in Lisbon while Amorim has delivered two Primeira Liga titles has been director of football Hugo Viana, the former Newcastle United midfielder who has been hugely successful in recent seasons at finding players and making huge profits for Sporting.

They were former team-mates at Braga, both have ties to lower-league Belenenses FC, and are so close that their wives are business partners together as interior designers. But now Amorim is heading to Manchester United for the ultimate football renovation project, while Viana is joining Manchester City in the summer.

Even Amorim himself sees the quirk of facing City in the Champions League in his final home match for Sporting. After facing Braga in a domestic game, he starts at Manchester United during the international break and will attempt to break City’s dominance in the Premier League.

“If the result [against City] is negative, expectations will drop; if we win they will think that the new Alex Ferguson has arrived,” he said ahead of facing Pep Guardiola’s team. “We expect a very difficult game, from the best team in the world, from the best coach in the world. An exciting, difficult game and we want to be competitive and win.”

Everything they touched turned to gold

Amorim’s appointment at Sporting four years ago was on Viana’s watch, when the young coach was in his early 30s and only had Casa Pia, hastily taken coaching badges and a short spell at Braga on his CV. The pair had been team-mates at Braga, at their famous stadium with a cliff edge on one side.

Viana’s early steps as a director of football was at Belenenses FC, where Amorim had started as a youth player. When Viana took up his role at Sporting, he was part of the team that recruited Amorim and everything they have touched since has turned to gold.

The list of transfers who have seen their valuations soar include Pedro Porro, whose deal was struck when he was on his holidays. Porro turned up to his unveiling in his denim beach shorts, which was the basis of memes when he started superbly in Portugal. Fans joked he had forwards in the pocket of his shorts.

Porro went to Tottenham Hotspur without much change from £40 million. Manuel Ugarte was taken from Famalicão and sold to Paris Saint-Germain for €60 million and will be reunited with Amorim at United. Amorim will also face one of his former players against City in Matheus Nunes, who moved to Wolverhampton Wanderers after his spell at Sporting.

Their current team includes Viktor Gyokeres, signed from Coventry City and now among the most sought-after strikers in Europe. Ousmane Diomande, 20, was brought over from Midtjylland, while Morten Hjulmand came from Italian club Lecce. “Manchester are in good hands,” said the Denmark midfielder, scorer of the equaliser against England at the Euros.

Pair formed perfect working relationship

Hjulmand was talking about United but the topic of conversation could easily have been City. Txiki Begiristain’s shoes are huge to fill as City’s director of football but Viana has built a strong reputation, having underwhelmed in the Premier League as a player with Newcastle.

While he scored a free-kick to ensure Champions League football, and also netted in the famous comeback against Feyenoord at Europe’s top table, he never lived up to his billing as one of the best young players in the world when he arrived on Tyneside.

His move to the Etihad Stadium has been built on his work with Amorim over the last four years, with the pair forming a perfect working relationship. Amorim would take the limelight, while Viana was happy working away quietly. He does not give interviews, while Amorim has been the front of house for Sporting.

But Viana is known to be seen on the training pitches, watching sessions and maintaining his strong relationship with staff. As a negotiator, he has been very effective. Sporting and Brighton were in for Conrad Harder from Nordsjaelland in the last window and Viana flew out to Denmark on the day after the English deadline had passed to secure the deal. There was still time in the Portuguese window but Viana did not want any clubs coming in and landing him for the January window.

Ahead of facing Sporting, Guardiola said: “I’m looking forward to speaking with him [Viana]. He is in touch with Ferran Soriano and Txiki [Begiristain] a lot and maybe in the next months or weeks we will be in touch. Hugo was the first choice, I didn’t intervene with this matter.”

The Manchester derby is less than six weeks away and while Amorim and Viana are in opposite corners now, their families will remain working together. Amorim’s wife, Maria Joao Diogo, owns Dois Tons with Viana’s wife, Raquel Gomes.

Dois Tons’ mission statement is to “create spaces with a unique identity” through their use of “color palette, textures and which are an extension of their history”. Amorim and Viana have been creating something unique at Sporting. Before Viana arrived at the club, they had not won a title in 18 seasons.

They leave with two titles won together and an open invitation to stay in Lisbon. “I spoke with the president,” said Amorim, on his decision to leave for United. “Whatever you decide, you always have the possibility to continue. If you change your mind can always speak to us.”

After their work in the last four years, Sporting’s duo could have worked together for years if Manchester had not come calling.