And waited. And waited some more. Well, they're still there. They've been within three points of the top of La Liga all season, and often first or second. And, having beaten Milan at the San Siro in the first leg of the Champions League round of 16, they are poised to advance after the return fixture on Tuesday night.
Overcome that hurdle and they will probably be arguably the only underdogs left in the quarter-finals. Galatasaray and Olympiacos - assuming they make it and it's by no means certain - may be "smaller" in absolute terms, but they are giants in their own countries - Galatasaray have won the most Turkish titles, including two of the last three, Olympiacos 15 of the last 17 Greek championships - whereas Atletico's achievements have been dwarfed by those of Real Madrid and Barcelona.
They've grown steadily since Diego Simeone's arrival, but few could have expected a season like this, particularly when you consider that in the past three summers they've lost the likes of David De Gea, Sergio Aguero and his replacement, Radamel Falcao, and, because of their huge debts, have operated on a shoestring.
Credit Simeone, above all. You could see him implementing a siege, underdog mentality but that schtick gets old. He's gone beyond that and created a cohesive, well-drilled unit that plays to its strengths. It's not rocket science, but they execute it extremely well. That often gets lost when folk focus on things like Simeone's intensity and passion.
The fact is, their success is built on an outstanding goalkeeper (Thibaut Courtois); an uncompromising defensive partnership (Miranda and Diego Godin); one of the most effective full-backs around (Filipe); an elegant, creative winger (Arda Turan); and a bright home-grown youngster (Koke). Oh, and Diego Costa, who has 27 goals this season. The Brazilian-born, newly-minted Spain international has been a one-man wrecking crew, particularly in the early part of the campaign.
Debts - to banks, the taxman and other clubs - and third-party owners mean it's difficult to see Atletico building on this next season. And, with a relatively small squad and not much rotation, you expect injuries and fatigue to catch up with them. But, for now, they're living large. "I'm not putting any limits on this season," Simeone said last week. "We were supposed to fold months ago. Well, we're still here, aren't we?"
If things don't turn around quickly, Arsene Wenger knows what's coming. He'll hear the words "I told you so" more often than he'd like. And people - possibly even the Arsenal fans who booed him on opening day, will once again wonder if he's past his sell-by date.
It's funny because in some ways it's when seasons begin and end that has left Arsenal in this position. In the 12 months (give or take) between March 8, 2013 and now, they collected 88 Premier League points - enough to win the title most years.
In cup competitions, they've gained wins over Borussia Dortmund, Napoli and Tottenham.
And yet three defeats in six games across all competitions before yesterday's FA Cup win over Everton tell their own story. A two-point lead at the top of the Premier League has turned into a four-point deficit and a home defeat to Bayern Munich has left them hanging on the edge of the Champions League precipice.
What will rankle Wenger is the lack of progress, and what will annoy fans is the notion that this could be avoided. Yes, injuries (Theo Walcott, Aaron Ramsey, Alex Oxlade-Chamberlain and now Jack Wilshere too) offer some mitigation. As does Mesut Ozil's tendency to disappear and reappear seemingly at random. The fact is things could have been even worse; had they lost one of the two centre-backs or Olivier Giroud, for example. But, as Wenger's critics have been saying all along, the money was there - why didn't he spend it?
According to a report from KPMG, there are more than 1000 third-party owned players in Europe. At top clubs in Portugal, such as Benfica and Porto, third-party stakes represent as much as 80% of the value of the squad. But we know about them because they are comparative marvels of transparency, owing to their public listing. When it comes to other clubs in other nations, matters get decidedly murky.
Typically, a third-party owner helps fund a transfer and then receives a share of the proceeds when the player is sold on. But in other cases he'll take "economic control" of a player he signs as a youngster and places at a friendly club who'll give him a shop window but, in case of sale, will hand over the entire proceeds. And on other occasions, you'll have a club needing some quick cash selling a portion of a player to a third-party owner.
The problem is that ultimately third-party ownership is predicated upon the player being sold outright at some point. If he becomes a free agent or isn't sold for the highest possible price, the third-party owner loses out. So he has an incentive to push the club into selling the player. That's when third-party ownership - which Fifa say is not illegal, though some countries have banned it - turns into third-party influence, which is a no-no.
"Third-party influence is not allowed, but I don't think Fifa have ever brought a case against anyone and yet we know it goes on," said Uefa general secretary Gianni Infantino. "It's something we're concerned about. Fifa have commissioned two studies and may commission another. That's great, but we want action."
It's especially a concern because there are investment funds out there - you can find them on the web - who act as both agents and third-party owners and, in some cases, represent managers and directors of football clubs as well.
Uefa have written to Fifa asking for an outright worldwide ban of third-party ownership. They're unlikely to get it because the practice is far too entrenched in Africa and South America. Instead, they'll probably get more inaction because it's something that Fifa, for political reasons, don't want to face.
If that happens, Michel Platini wants a ban in Uefa's 54 member nations. His message to Fifa? "If you don't do something, we will." He is likely to have enough support to do so and might well score some political points with an eye towards the Fifa presidency in 2015. Assuming, of course, he decides to run.