The Italian played a crucial part in securing the man who is now... playing a crucial part in their Premier League title bid.
And the Blues may have more to thank the 44-year-old for at present than they realise.
Indeed, while Jose Mourinho is the mastermind behind Chelsea's current Premier League title bid - during his short spell in the Stamford Bridge dugout, Di Matteo was nowhere near as effective in the top flight - there is another crucial factor driving the west London side's recent success.
That factor is a certain Eden Hazard. And what was the crucial factor behind his decision to join Chelsea?
The small matter of the Blues being the European champions the summer he moved to the Bridge. Imagine what would be of Chelsea now had they not triumphed that night - led by Di Matteo - in Munich?
The Premier League leaders would no doubt have found other quality buys, just like they did with Cesc Fabregas, Diego Costa etc. But Hazard is one of the best players in the world. Had he joined Manchester City, United or Arsenal, the landscape of English football may be very different today.