Costa scoring his seventh goal in nine matches in such dramatic circumstances wasn't the story, though. It's Chelsea's failure to once again pick up three points that remains the talking point around this team.
Interim boss Guus Hiddink has seen his side draw six times in the 10 games he has been officially in charge. Just two of his four victories have come in the Premier League, meaning the Blues have picked up a mere 12 points from an available 24.
Compared to the last eight league games of Jose Mourinho's reign, it's an increase of five points—the former manager's Chelsea won two, lost five and drew once, against Tottenham Hotspur.
It's an improvement, but it's still not great. It's still not enough to get Chelsea into the top 10 and comfortably away from being dragged into a potential battle at the foot of the table.
A big reason for the changes we've seen has been the John Obi Mikel-Nemanja Matic combination in midfield.
Hiddink's intentions have been clear in the early weeks of his second spell in charge at Stamford Bridge; he needed to stop that losing habit, which he has.
He hasn’t transformed those defeats into victories, however. All these draws Chelsea are recording aren’t enough to save their season.
The Dutchman needs to take the next step on the road to recover; his challenge is to get this team firing properly and winning games consistently.
To do that, Hiddink must turn his back on the one thing that has made Chelsea hard to beat again—Matic and Mikel's partnership.
We saw why when United visited Stamford Bridge; Chelsea were back to playing with the handbrake firmly on.
That tactic worked against Arsenal at the Emirates Stadium a few weeks back as the Blues were able to set up in a way that stemmed Arsene Wenger's men. By controlling those central areas, the Gunners couldn't get through, and it led to Chelsea dominating the game, even when it was 11 versus 11.
When they're at home facing a struggling United side, though, Chelsea have to get at them and make the most of their advantage. They can no longer play so restricted as games are running out in the league.
Chelsea need points to climb the table and draws aren’t delivering them at the required rate.
Louis van Gaal had the laborious Michael Carrick and Marouane Fellaini anchoring his own midfield on Sunday. A lack of dynamism from Chelsea meant the pair looked comfortable, rarely pulled out of position by the players opposite them who were performing the exact same role.
It was similar at Vicarage Road in midweek when Chelsea endured a goalless draw with Watford. The Hornets had lost four of their five league games since the Boxing Day draw with the Blues, but Hiddink still erred on the side of caution.
Regardless of league positions, it was a game of Premier League champions against the Championship runners-up, yet you wouldn’t have known it. The caution hints at confidence remaining fragile, although it’s only by instilling belief in his players that Hiddink will get the best out of them in an attacking sense.
He can give them long speeches to that effect, or the interim boss can alternatively field a team that shows he’s confident in the players’ abilities.
Like United on Sunday, Watford were there to be got at. As remained the case in both games, it was only until the final 20 minutes or so that that Chelsea upped the ante and played with anything resembling ambition.
Dropping four points within the same number of days, the coin has flipped. From being about damage limitation, Matic and Mikel playing together is damaging Chelsea's season further.
It helps that Eden Hazard is back from injury. Hiddink’s hand has partly been forced while the Belgian hasn’t been fully fit.
Chelsea’s squad lacks the same depth of those teams we considered their rivals for honours at the start of the season. Whereas Manchester City have players in reserve to combat the loss of their own dynamic Belgian in Kevin De Bruyne, for instance, Chelsea don’t.
A big part of their dramatic fall from grace this season has been Hazard’s lack of form. He was their talisman as they cruised to the Premier League title. It’s been much different this season and they have suffered.
Hazard is speaking a different language now. From being relatively silent while the chaos ensued around him before Mourinho eventually lost his job, the Belgian is saying all the right things in the present.
In a recent interview with the Guardian, Hazard said:
For a team of champions to go through what we have this year even I can’t explain.
Things have been better recently, but we’re still not winning games quite as we used to. No one can put his finger on what’s happened at Chelsea.
[…] I’ve never been one to deliver speeches in the dressing room, like a John Terry, Frank Lampard or [Didier] Drogba, but I’ve always tried to lead in my own way on the field: demanding the ball, trying to make a difference. The day I’m 100 per cent again, I’m convinced Chelsea will perform better too.
Those improved performances will only come with a less rigid midfield pairing. Either Mikel or Matic has to be sacrificed in the name of Chelsea’s season.
Averaging two points a game under Hiddink, Chelsea’s current form suggests they’ll finish the campaign on 50 points. That’s enough to avoid a relegation dogfight—which, like it or not, will remain at the back of Chelsea’s minds until they pass the magical 40-points mark—but it will mean they just about scrape into the top 10.
A club of Chelsea’s size and stature has to have bigger ambitions than that. The responsibility lies with Hiddink to implement it.