The Blues activated the Senegalese striker's release clause of approximately £7 million to bolster their attacking options, adding much needed quality and quantity to the forward line.
But what will Ba's arrival at Stamford Bridge signal in terms of tactical change for Rafa Benitez's charges?
Fernando Torres has played a lot of games this season.
With no other options up front except chancing Victor Moses or the failed Eden Hazard experiment in Turin, the Spaniard has started 27 games so far.
Whether he's good or bad for the team, fits or doesn't fit in the system, it's pretty obvious that he's knackered and needs a few days to put his feet up.
Ba's arrival will grant him that.
One of Chelsea's biggest problems this season has been a lack of presence inside the penalty area.
At times, it looked like the Blues had acquired a big, long list of transfer targets with attacking midfielders at the top—only, as the club got to the halfway point in that list, they ran out of money.
The result? Eden Hazard, Juan Manuel Mata, Oscar, Victor Moses and Marko Marin all vying for the same spots, while Fernando Torres is left to fly the forward's flag on his lonesome.
Torres has a habit of "getting involved" in the build-up play, meaning the intricate passing between him and the advanced midfielders hits a dead end when there's no striker to finish the move.
The addition of Demba Ba will create a clear and much-needed divide: strikers here, midfielders there.
Demba Ba is not the next Didier Drogba, but he's as close as you're going to get for £7 million.
Drogba was the man whom Chelsea leaned on to dig them out of a hole. He often came up in the clutch, and his size allowed his teammates to play fruitfully off him when forcing matters.
Since the Ivorian left, Chelsea don't know where to look when they're desperate.
Again, we reiterate that Ba is no Drogba, but having a big-bodied target man to hit is an option almost every team needs.
Chelsea have plenty of able crossers, but not a lot to aim at.
Fernando Torres leapt like a salmon to head home against Aston Villa, but he was aided by a defensive miscommunication that enabled him to rise unchallenged.
One-on-one, in the air, Torres is subpar. The same cannot be said for Demba Ba, who wreaks havoc in that area.
Cesar Azpilicueta is full of decent crosses and now, finally, has someone to aim at. It also gives Juan Manuel Mata and Eden Hazard a slightly less precise ball to play, which will ease their task considerably.