It was a sobering moment for Chelsea fans when the referee's final whistle blew at Stamford Bridge on Saturday.
Mike Dean's final action of a game filled with controversy and incident was the death knell for Chelsea's title hopes.
That 2-1 defeat to Sunderland was difficult to stomach, and it will continue to frustrate anyone associated with Chelsea for some time yet, especially after it handed significant momentum to rivals Liverpool in the title race.
Suddenly the air of invincibility of Chelsea and their manager, Jose Mourinho, at Stamford Bridge has been lifted.
It was 77 games unbeaten in the Premier League until Fabio Borini's penalty did the unthinkable and won the game for the relegation-threatened Black Cats.
Records can come and go, but it will be some time before we witness another that will have such an impact like Mourinho's did.
His unbeaten record at Stamford Bridge was significant. It was a major weapon in the psychological battles that ensue before kick-off. Now it's gone.
How do Chelsea replace it? Well, with Diego Costa, of course.
It's been discussed all season, filled column inches, been shouted from the terraces and debated excessively—Chelsea's strikers simply aren't good enough.
With the form of Eden Hazard and Chelsea's excellent defensive record, there was a moment when we thought the Blues may well have got away with it, but time has caught up with them and recent weeks have confirmed where their title bid has always been weak.
This season is gone in terms of domestic success. Chelsea need to target invincibility again with next year in mind, and however many millions it may cost to get him, Diego Costa needs to be signed to bring it back.
It's a fact in football that reads simple on the page but is so much more difficult in practice—scare your opponents with firepower and invariably you will succeed.
Diego Costa can emulate them all.
The Spaniard's record over the past two seasons has been phenomenal—55 goals in 80 games outlining the consistency he has added to his undoubted skill and threat.
Such goalscoring form strikes fear into the heart of opponents, gives his team-mates confidence and ultimately wins matches.
Chelsea are almost there when we consider them being the complete package. Mourinho will need to make some minor tweaks elsewhere in his team, but it's in attack where he will need major surgery.
Diego Costa will not be able to do it all himself, yet he will transform the Blues' fortunes significantly.
The reaction among Chelsea fans to him being fit ahead of their Champions League clash with Atletico Madrid on Tuesday outlines that fact.
As The Guardian reports, Diego Costa has recovered from a gashed leg in time to face Chelsea at the Vicente Calderon Stadium, and the news has dented confidence for Blues fans.
They know how significant his presence will be. Atletico have other threats, but their No. 19 is the talisman. He's the match-winner.
With him wearing the Blue of Chelsea, it's difficult to imagine them not winning more matches next season.
Chelsea are good; Diego Costa will make them great.
Garry Hayes is Bleacher Report's lead Chelsea correspondent and will be following the club from a London base throughout the 2013-14 season. Follow him on Twitter here @garryhayes