FC Barcelona and Atletico Madrid have already seen plenty of each other this season, as this UEFA Champions League quarter-final tie will present the fourth and fifth time both clubs will be facing each other.
No winner emerged in any of the three previous matches, illustrating how competitive these next two matches should be. With so little separating both teams, every minor detail could become a major factor in the outcome of each game.
Here are some of the biggest factors that will decide the winners of this contest.
Health is always a factor when it comes to sports, and in this particular tie, it could end up making all the difference.
With both clubs so evenly matched, both matches could come down to one or two crucial stops by each team's respective goalkeeper, and as reported by Football Tweet, Barcelona will be without their star man, Victor Valdes:
Jose Manuel Pinto is expected to replace the Spanish international, and while the veteran is a solid stopper in his own right, he's no Valdes.
Atletico's Thibaut Courtois, meanwhile, is healthy enough to do this:
Iker Casillas and a healthy Valdes are two fantastic stoppers capable of deciding matches on their own, but Courtois is the best stopper in La Liga right now, and some would even make the case he's the best in all of football, period.
In a battle between him and Pinto; there's no contest. The Belgian youngster has made a living out of making vital stops for his team all season, winning Atletico countless valuable points in the process.
No matter how you spin things, having Courtois is a major advantage for the visitors going into this match, and a healthy Valdes would have negated that advantage considerably.
Barcelona must hope this game doesn't turn into a defensive struggle, because it's clear which of the two stoppers would be most trustworthy in those circumstances.
Fans of other teams often find Cules conceited or arrogant, but by definition, you can't be conceited if the club you support is simply that good. Barcelona are used to winning, and as a result, fans will be very critical of their team and even more critical of yours.
They also happen to form one of the best supporting groups in football. Anyone who's ever been to Camp Nou will tell you it's impressive. The sheer size of the stadium coupled with the vocal support of the fans make for very difficult circumstances for any visiting team.
Barcelona have ruled La Liga for the past few years, and Atletico are those pesky new kids on the block who simply won't acknowledge who's in charge. You can be sure the Camp Nou will be rocking on Tuesday, as this will already be the fourth chance La Blaugrana will get at putting the Atleti in their place.
Whether the atmosphere will be as good as during the Clasico remains to be seen, but expect the place to be loud regardless.
How Atletico handle the crowd and the impressive surroundings during the first leg will be vital, as Barcelona would like nothing more than to go for the jugular early and make sure this tie is well and truly over before the team has to make the trip to the Vicente Calderon.
Depth and Experience
This last one is very simple: Barcelona have been here before and are built to compete on several different fronts at the same time. Atletico are not.
The visitors lead the race for the La Liga title and are in the midst of an impressive run of results, and while Diego Simeone's squad is supremely talented, it lacks the depth of some of the top squads around Europe.
That's not to say Atletico don't have depth—they do. In fact, they have excellent depth. Just not on the same level as Barcelona. And in a long season filled with matches in both La Liga and the Champions League, this is traditionally the time of year when a difference in depth starts to show.
BBC's Andy West mentioned Atletico's depth at the start of the season, and so far, Simeone and his troops have proven all of us wrong:
Atletico have been growing as a club for years now, and becoming a top club is a process. This is the first time the club has been this close to a major title on several fronts this late in the season, and for most of the players, it's also the first time they've been within touching distance of both trophies.
If Atletico can handle the pressure Barcelona have gotten so used to, and if they can work around any potential injuries or issues with form, the club should be fine in this tie.
Unfortunately, that's a pretty big if.