The Teessiders join north east rivals Sunderland in dropping to the Championship after failing to avoid defeat against Antonio Conte's side, who are just one win away from winning the Premier League for a fifth time.
Goals from Chelsea forward Diego Costa and midfielders Marcos Alonso and Nemanja Matic condemned Boro to defeat and relegation after just a single season in England's top-flight.
Steve Agnew's men have now been relegated from the Premier League for a record-equalling fourth time, and can have no complaints about their fate. After the match, Agnew spoke about the deflated feeling in the Boro dressing room and said the club simply came up short.
"I mean, everyone is devastated," Agnew said. "We've worked so hard for a number of years to get back into the Premier League, and we know how tough the Premier League is.
"Obviously we've pulled up short. I've left a very silent dressing-room with everyone, staff and players, absolutely gutted. We can only reflect over the 36 games we've played. We've not won enough games or scored enough goals."
Middlesbrough have only scored 26 times this season, the same as fellow relegated side Sunderland.
In a torrid season, the one-time Uefa Cup outfit have only managed 94 attempts on target throughout the entire campaign. Chelsea, meanwhile, the team who sealed their somewhat inevitable fate, have managed to net 46 in their home games alone.
There is only one spot left to be filled in the relegation zone, and although five teams are still not mathematically safe, it looks like Hull City, Crystal Palace or Swansea City will be the ones to join the beleaguered north east sides. Marco Silva's men could go down if they lose to Palace at Selhurst Park on Sunday (14 May).