Milan edged their way though group H alongside Barcelona, while Atletico thoroughly dominated in group G, taking 16 out of 18 possible points.
While not a traditional powerhouse, Atletico has broken through on the world stage in a big way this year, as they are currently joint-top of the table in La Liga with Barcelona and Real Madrid. Indeed, they have taken four out of six points against those two sides so far in the league, indicating Simeone has instilled a fearless attitude in his side.
Milan's issues have been well-chronicled, with financial issues forcing the sale of many of the club's top players over the past several years. The retirement and departures of club legends have also contributed to the team's downfall in the past two seasons.
However, Milan impressively qualified for the Champions League on the final match day in Serie A last season, and they have once again made it into the knockout stages, highlighting a tendency for the side to step up in European competition.
As Clarence Seedorf prepares his side for what is sure to be an enterprising attacking side on Wednesday, several of his players must stand out for Milan to have a chance at progressing.