Madrid, April 23 : They both wear red and white and have similar names, but the relationship between two of Spain's oldest clubs is more formal than other such rivalries. The clash between Atletico de Madrid and Athletic Club de Bilbao is not only a huge game because it features two sides currently inside the top five of La Liga standings, but also a duel between two clubs with a lot in common.

While many people know that these two clubs both wear red and white and both have similar names, not everyone knows that their relationship is more formal than that.

Atletico de Madrid was established back in April 1903 as Athletic Club de Madrid, with the founders being Basque fans of Athletic Club de Bilbao, who were studying in the Spanish capital and who wanted to maintain the connection with their team. Athletic Club de Madrid naturally took their colours from their 'parent' club, which had been established five years previously. Both initially wore blue and white chequered shirts, before switching to their current red and white stripes in 1911 after famously receiving a set of jerseys originally made for English club Southampton.

The two Athletics were so close during their early years that they were not allowed to meet in official competitions. They even shared players at times -- the Madrid side's star forward Manuel Garnica Serrano was 'loaned' to the Basques for the 1911 Copa del Rey final and he scored against CD Espanyol of Barcelona.

As Spanish football gradually became more formalised and professional, the two Athletics drifted apart. In 1921 the Bilbao side was crowned national champions after a 4-1 win over their Madrid 'brothers' at San Mames. Full autonomy was well established by the time they both became founder members of La Liga in 1928/29. The first top-flight meeting came on April 7, 1929, at the Estadio Metropolitano in Madrid, with the visitors winning 3-2.

Games between the two have often been fiercely contested through the decades, as most sibling rivalries can turn heated at times. A famous 6-6 La Liga draw in January 1950 saw Moroccan-born Larbi Benbarek among the scorers in a last-gasp Atletico de Madrid comeback.

Athletic Club's 4-1 victory at San Mamés with 10 men in October 1982 was a key victory on the way to winning that season's La Liga title. A 2-1 victory at San Mames in April 2014 has been acknowledged by current Atleti coach Diego Simeone as the moment he knew his team had what it took to take home that season's La Liga crown.

There have also been famous meetings in other competitions. The 1956 Copa del Rey final saw Athletic Club win 2-1 in Madrid. And Atletico de Madrid came out on top 3-0 when the two rojiblanco teams met in the 2011/12 Europa League final in Bucharest, their only meeting to date in UEFA competition.

Connections between the teams continue to this day. Former Athletic Club sporting director Jose María Amorrortu was academy director at Atletico de Madrid from 2006 to 2011, working with current first-team stars such as Koke, before moving north and helping to develop local Basque talents including Iñaki Williams and Iker Muniain.

Current Athletic Club player Raul García made 216 La Liga appearances for Atletico de Madrid between 2007 and 2015. The Pamplona-born midfielder's goal in a 1-1 draw at San Mames some seasons ago means he is one of very few to have scored for both sides in the fixture.

The sibling rivalry continues this Saturday at the Estadio Civitas Metropolitano when Simeone's side takes on Ernesto Valverde's Athletic Club in a La Liga match. Fans and players from both teams will enjoy the occasion, although past connections will count for little with three points at stake.

/IANS