Jose Mourinho and Sir Alex Ferguson began their coaching duel in 2004, when Mourinho's Porto took out Manchester United on their way to the most unlikely of Champions League triumphs.
For Mourinho, it was a defining victory that made everything possible. For Ferguson, it was the latest in a run of European failures and marked one of his most miserable seasons at Old Trafford.
Mourinho has since led Chelsea and Inter Milan teams against Ferguson's United, and on Wednesday will be up against his old friend as the under-fire coach of Real Madrid.
Mourinho's enigmatic team, for all their sparkling star power, are cut adrift of Barcelona and behind city neighbors Atletico in the Liga table. The title race is as good as over.
The same is true in England, where Manchester United have opened a 12-point lead over Manchester City and Ferguson is staring down a 13th title. The 71-year-old, written off so many times in his 26 years at Old Trafford, is as hungry as ever and has built yet another impressive team.
Domestic matters will be put aside this week, as Mourinho and Ferguson revisit a rivalry that has thus far been dominated by the Portuguese. Mourinho has won of six of their 14 meetings; Ferguson just two (or three if you count the one on penalties).
Here's the game-by-game story of the Mourinho vs. Ferguson coaching battle so far...