Costa’s strike was enough for a 1-0 victory and sent the Blues top of the Premier League at the Riverside Stadium, ahead of Liverpool and Manchester City.
It was the sixth successive game Chelsea have avoided conceding, with Antonio Conte’s side scoring 17 goals of their own in that time – three more than the next highest scorers over that period, Liverpool.
Costa had a tough second season at Stamford Bridge, only managing 12 Premier League goals in Chelsea’s whimpering title defence, but he is already close to surpassing that this season and is two goals clear of nearest rival Sergio Aguero in the race for the Golden Boot.
The Spaniard’s behaviour and temperament has often been called into question but Conte insisted he is delighted with the 28-year-old’s attitude and he must carry on with what he is doing.
"For me, it's important to have this type of question because in the past, you asked me about his behaviour, about his reaction, about his patience," Conte told Sky Sports News.
Middlesbrough vs Chelsea player ratings
Middlesbrough vs Chelsea player ratings
1/22 Middlesbrough: Victor Valdes - 7 out of 10 out of 10
He made a number of crucial saves throughout, and in regard to the goal, he was left helpless following a defensive error. It was a good performance from him today.
2/22 Antonio Barragan - 6 out of 10
Looked very promising from the start, with his diagonal through balls causing problems for the Chelsea defence.
3/22 Calum Chambers – 7 out of 10
Made a number of vital clearances that saved his side at times, looked strong in his tackles and worked well from the back out.
4/22 Ben Gibson - 5 out of 10
It was a mediocre performance from Gibson today. He worked hard, but was wasteful in possession at times.
5/22 Fabio - 5 out of 10
There was a feeling of confidence about his performance today, and it showed in his movement and passing. However, he was going missing at times.
6/22 Adama Traore - 7 out of 10
His pace caused Chelsea problems when he charged at them. He’s a powerful player with an eye for attacking and this should have been used to more of an advantage for Boro.
7/22 Adam Forshaw - 6 out of 10
His work rate was faultless today and he really appeared to find his feet as the game progressed.
8/22 Adam Clayton – 5 out of 10
He showed glimpses of brilliance when on possession, but was quiet for the majority.
9/22 Marten De Roon - 6 out of 10
He was a battler throughout and used possession well. However, he was clumsy in a few of his tackles which was unnecessary. 6 out of 10.
10/22 Gaston Ramirez - 6 out of 10
He was a key element to the Middlesbrough attack, but aside from this he was persistently giving away fouls.
11/22 Alvaro Negredo – 5 out of 10
Aside from his late chance which tested Courtois, it was a relatively quiet performance by a man of such high standards.
12/22 Chelsea: Thibaut Courtois – 6 out of 10
He had very little to do today, except one late strike from Negredo.
13/22 Cesar Azpilicueta – 5 out of 10
Looked dangerous going forward, but gave away a number of silly fouls.
14/22 David Luiz – 6 out of 10
He was very physically strong today and done well in the air.
15/22 Gary Cahill – 6 out of 10
It was a classic Cahill performance today. Played well, tackled well and used possession well from the back.
16/22 Victor Moses – 8 out of 10
His impact on the team is phenomenal. He’s quick, clever on the ball and an absolute powerhouse – great game for him today.
17/22 N’Golo Kante – 7 out of 10
He worked well with Moses, creating numerous chances and deliveries into the danger zones.
18/22 Nemanja Matic – 6 out of 10
He was at the heart of a number of Chelsea attacks today. His passing was faultless, but was caught out of position occasionally.
19/22 Marcos Alonso – 6 out of 10
Made a few bad decisions when in possession, but aside from that he worked well today and created a few chances.
20/22 Pedro – 7 out of 10
His work rate was faultless and he came very close to getting himself on the scoresheet, only to be denied by the crossbar.
21/22 Diego Costa – 8 out of 10
His goal was an example of his true poaching nature as he pounces on the first Boro mistake. Great performance all round from him today.
22/22 Eden Hazard – 7 out of 10
He created a number of chances throughout and was a key element to the Chelsea strikeforce.
"Now I think he is one of the best strikers in the world and he has to continue in this way, showing his patience, but in the right way.
"He is very focused on the team, to help the team with the ball, without the ball and he is scoring a lot of goals. He has to continue so.”Reuse content