Atletico Madrid 4 AC Milan 1: Diego Costa fires Atletico into the big time, and proves Diego Simeone's side can compete with the best in the Champions League

The Spanish side must now be considered genuine contenders to win the Champions League, as well as La Liga

Atletico Madrid's Brazilian-born forward Diego Costa (C) celebrates after scoring during the UEFA Champions League quarter-final second leg football match Club Atletico de Madrid vs AC Milan (GETTY IMAGES)

Not so long ago Diego Simeone derided his side’s chances of ever upsetting the Spanish duopoly of Barcelona and Real Madrid. Atletico Madrid, and indeed fellow third-place chasers including Athletic Bilbao, Real Sociedad and Valencia, were just a sub-story to La Liga’s usual two-horse Clasico race. A task of being the best of the rest, no-hopers in their quest for glory on a big scale.

Maybe it was a genuine concern or maybe it was a challenge laid out to his troops - an ‘us against the world’ mentality. Either way, Atleti have proved they can challenge for top honours not only in Spain, but against the best clubs in the world. Tuesday night’s 4-1 victory over seven-time European champions AC Milan, which gave Simeone’s side a 5-1 aggregate victory in the Champions League last-16 stage, shot Atleti into the big time. A convincing victory over one of the beasts of European football and a place in the quarter-finals for the first time in 17 years. This Atletico Madrid side are no longer just the bridesmaids, they mean business.

“No, absolutely no,” Simeone said in response to a question regarding his side’s title chances last August. “Madrid and Barcelona play in a different league. This is a boring championship for the rest of the supporters who can only aspire to be third or fourth. We’ll have to wait for a different distribution of television money because now the league is only of two.” The Argentine’s comments came after his side’s first loss of the season against Espanyol and may have been raw, but there was a deep-lying concern there.

That was almost five months ago. Now, with the season two months from its conclusion, Simeone has guided his side to second in La Liga, three points behind neighbours Real and a point above defending champions Barcelona, and into the last eight of arguably the strongest club competition in the world.

Atleti’s rise under the Argentine has been the success story of Spanish football since his installation in December 2011, succeeding Gregorio Manzano at the club he was worshipped as a player in two separate spells. After a long absence, Atleti are being taken seriously again and their Copa del Rey final success against Real at the Bernabeu last season cemented their presence as a real threat to Spain’s ‘big two’. For much of the last campaign they also posed a serious threat in the league, too, before tailing away at the conclusion.

There were questions as to whether that threat would prolong into another campaign, such were the big bucks spent at the Bernabeu and the Camp Nou but Atleti have continued to be the noisy neighbour - and have gone a step further a year on. The club from beside the Manzanares now have a genuine chance of winning La Liga but they also have a chance of doing what many believed was unthinkable just two years ago by lifting the trophy their neighbours have won nine times and so desperately want for a tenth.

Such was Tuesday night’s victory over the Rossoneri that the near-55,000 crowd inside the Vicente Calderon took part in a Mexican wave with the clock ticking down - a surefire sign that the damage has been done and all, except the 2,000 or so fans tucked away in the north stand that made the trip from Italy, approved of a good night’s work. This is not the Milan of the 1980s, nor is it the Milan of the 1990s or the early 2000s, but it was Milan, a side used to being seen in the latter stages of the competition and a side that has lifted the trophy seven times. Atleti swept them aside with ease.

The foundations had been put down in the San Siro three weeks prior to the second leg when Diego Costa’s goal ensured Los Rojiblancos returned to the Spanish capital with the advantage and with a crucial away goal. A game plan that had worked perfectly in a stadium Simeone had called home with Inter between 1997-99. The tie had been billed as one of the closest of the last-16 but Costa’s goal ensured Atleti had the favourites tag back on home soil and ensured, eventually, that the tie was anything but even.

Milan are a side in transition, to put it in basic terms and to put it mildly. Clarence Seedorf has taken charge of a misfit Milan side and the job is not one that can be completed overnight, it’s a work in progress. But Milan still had the world-class Mario Ballotelli and Kaka within their ranks, players that can haul a goal from nothing - a trait that would be needed on the biggest stage and that would be needed against a usually tight Atletico defence. Simeone’s strongest back-four of Juanfran, Diego Godin, Miranda and Felipe Luis has forged one of the best defensive partnerships in Europe, something showcased on the biggest stage with just three goals conceded in the competition up until Tuesday - the best record in the competition.

Despite the quick-fire start that saw Costa open the scoring early on that defence looked anything but secure as former Real man Kaka got Milan on level terms before wasting another golden opportunity from an Adel Taarabt cross with the score at 1-1. It was a big moment and Atleti rode their luck, but it was a moment that has been the exception rather than the rule this season and the hosts made Seedorf’s men suffer for their missed chances with a deflected second from Arda Turan before goals from Raul Garcia and a second for Costa sealed Atleti’s historic win.

It ensured they were the first Spanish club to quality for the quarter-finals, although Real’s progression seems only a formality with a 6-1 lead over Schalke heading back to the Bernabeu next week and Barca are in pole position to go through with a 2-0 lead over Manchester City, and it will be their sixth time at the last-eight stage. They joined Bayern Munich in the hat for the next round and European giants including Paris St Germain, last year’s finalists Borussia Dortmund and Spanish rivals Barca and Real are expected to be possible opponents in the next round. Atleti are back in the big time.

Not that ‘Cholo’ Simeone will let his men get carried away. “It's a good time, but as we are living it now, it would not stop me to imagine and enjoy it, it is not time for that,” he told the gathered press post-match. “We expect dangerous and difficult quarterfinals. We need to rest and prepare to continue this work that we know we are doing well and that it is the result of the work of the whole team.” If there is a man to keep Atleti grounded it’s Simeone. Espanyol visit the Calderon on Saturday and there will be little talk of Tuesday night’s success story when the players return to training on Wednesday - the focus will be firmly on the weekend.

The draw for the next round doesn’t take place until the full round-of-16 matches are complete next week but Atleti will not be daunted by their prospective opposition. Another European ‘big boy’ will await but Los Colchoneros have not shied away in the big games this season - far from it. In three matches against Barcelona Atleti have not been defeated, with Barca only claiming the Spanish Super Cup on away goals following two draws and a draw at the Calderon coming in the league. Atleti saw off their more illustrious neighbours at the Bernabeu earlier this season and held them to a 2-2 draw on home soil earlier this month. A Copa del Rey exit over two-legs was a blot on that copybook but the league meetings show a fairer reflections on their abilities this season.

One thing is for sure - nobody will want to face Atletico Madrid in the quarter-finals. The side known as the Mattress Makers have sewn together a winning patchwork this season and the stitches show no sign of coming apart.