When Chelsea defeated Atletico Madrid at the Wanda Metropolitano in the group stages of the Champions League earlier this season, it was heralded as one of the great Champions League triumphs. The Blues were not expected to travel to Spain and come away with a win against a side who have been a common feature of the latter stages of the Champions League in recent years - reaching the final in 2014 and 2016 - but they played fantastically and warranted their victory.But Antonio Conté's team are a good side - why was there such a reaction to this win? In a way, it is a compliment to Diego Simeone's Madrid side, and rightly so.Simeone - a man often touted as Arsene Wenger's eventual successor - has taken Atletico from the shadow of their city neighbours Real Madrid and turned them into one of the most feared teams in Europe. Now, he is within reaching distance of the trophy that announced himself as a top manager, and shot his side into the stratosphere: the Europa League.In 2012, Atletico defeated Athletic Bilbao in Bucharest to win Europe's secondary competition and haven't looked back. Like the Gunners, they would ideally like to be back in the running for a competition they have become very accustomed to in recent years. Atletico found their way into the Europa League following a tough Champion League campaign that featured the aforementioned Chelsea and AS Roma - who now find themselves in a semi-final match against Liverpool in the competition - and Azerbaijan champions Qarabag. In the group stages, Atletico didn't perform up to their own high standards, finishing in 3rd place with 4 draws, 1 loss and 1 win (an impressive 2-0 dismantling of the Romans). 3rd place meant that they were in the Europa League and they immediately became competition favorites.One almost feels sorry for the side that got drawn with them in the round of 32, it really was the worst possible draw. That side was Copenhagen, and they did not stand much chance - a 4-1 away win and a 1-0 home victory meant that Simeone's side was in the last 16.Locamotiv Moscow - the side currently at the summit of the Russian Premier League - were the next to face the behemoth's of Madrid, and they also didn't fair greatly - a 3-0 home win effectively ended the fixture, but that didn't stop Madrid from travelling to Moscow and hammering the Russians 5-1 to make the game 8-1 on aggregate and cement a place in the quarter finals with little hassle.The previous set of ties represented Atletico's toughest knock-out round test yet when they were drawn against Sporting Lisbon. The first match was traditional Madrid: rock-solid at the back and well-worked opportunities, that led to a 2-0 home victory and a good platform for the second leg. It wasn't that easy for them though, and it provides perhaps the best look at how a side could go about finding the chink in Madrid's armour. Lisbon, needing a win, got just that - a 1-0 victory in Lisbon had Madrid sweating, but they held firm. The Lisbon loss is definitely the result to focus on when interpreting how Simeone and his side can be taken on. The first leg of Arsenal's tie is being played at the Emirates Stadium and this home advantage needs to be made the most of. A defense that plays home to world class players such as Diego Godin, Juanfran and Stefan Savic - as well as the expert goal keeping talents of Jan Oblak - proved to hard to break down for Lisbon, despite Fredy Montero putting them ahead early on and giving them a good opportunity to progress. The way this defense performs - and has performed for years - is a intimidating on it's own, but they in attack, they are not short of talent either - including one of the most sought after players in the world, French forward Antoine Griezmann. Griezmann is one of the most terrifying offensive threats in Europe. The 26-year-old is always highly linked with transfers to the likes of Barcelona and Manchester United, and one feels if he performs well at the World Cup he may be on his way to a new team - with one of the largest transfer fees ever requested, no doubt. With this being the case, he and Atletico will be looking to go out on a high this season, whether Griezmann is to part ways or not. Quality players can be found all over the pitch in addition to those mentioned. Koke and Saul Niguez are two of the best midfielders in Spanish football and Premier League fans are all too familiar with strikers Diego Costa and Fernando Torres, both back now playing with the side that effectively made them the players they are. In the league, the Spanish giants have been the only discernible threat for the all-dominating Barcelona this season, and currently sit in second place with 6 games remaining, although the Catalans name is already effectively on the trophy as they have an eleven point advantage.After being knocked out of the Copa Del Rey by Sevilla, the Europa League represent Simeone's last realistic chance of silverware for the campaign. Even though there Champions League status is confirmed for next season - unlike Arsenal - they will want to add some silverware for the season. Considering how successful they have been in recent years, it is perhaps surprising that Atleti have not added to their trophy cabinet since the La-Liga victory in 2013/14. With Arsenal and the winners of Red Bull Salzburg vs Marseille the only roadblocks between them and once again claiming the Europa League the only factors in the way of amending this, they are a side to fear.From the moment Atletico entered the Europa League at the Round of 32 stage they were undoubtedly the team to fear. Now, as they prepare to take them on at the Emirates on Thursday the 26th, Arsene Wenger and his side must be resilient but also adventurous in the face of the tournament favorites. If Arsenal can defeat Atletico Madrid over two legs, then they deserve to be Europa League Champions. It won't be easy though.