Boro fans urge captain Jonny Howson to shoot from 20 yards and they probably regret it as he scoops the shot miles over.

Scott Large: Why is Lukaku's form at Chelsea such a shock? This is exactly what he was like his last season at Man Utd.

Gary Rose
BBC Sport at Riverside Stadium

Marcus Tavernier's free-kick could have been going in. Chelsea's players were certainly appreciative of Romelu Lukaku's intervention as he received several slaps on his back and pats on his head before the corner.

There's a bit of a languid style about Lukaku's play but he's got the goal - which makes him Chelsea' top scorer for the season with 12 - and played a crucial role defensively as well.

Only Trent Alexander Arnold (16), Andrew Robertson (13) and Bruno Fernandes (13) have registered more assists among Premier League players in all competitions this season than Mason Mount (11).

Jermaine Jenas
MOTD2 pundit & former Tottenham midfielder on BBC One

Good little spell this for Middlesbrough.

Chris Wilder will be happy with his team's response to going a goal down.

Boro try a short corner but there's a communication mix-up and it comes to nothing.

A bit of panic in the Chelsea box from the corner but they get it clear.

Boro come back again and win another corner.

Marcus Tavernier whips in a free-kick from the wing, it might even be a shot, but Romelu Lukaku heads over for a corner.

Chelsea defender Malang Sarr fouls Matt Crooks just before he can cross with several Boro players in the box. Free-kick.

A nice passing move round the box by Boro but Matt Crooks can't find striker Folarin Balogun with the final ball.

Middlesbrough haven't had a shot yet a quarter of the way through the tie.

Chelsea’s Romelu Lukaku has had a direct hand in four goals in his four appearances against Middlesbrough (three goals, one assist).

Christian Pulisic tries to cut inside Anfernee Dijksteel in the box but the Boro defender holds his ground and the hosts come away with the ball.

I did think Romelu Lukaku's lack of celebration was unusual. Was wondering if I'd forgotten a loan spell he had at Boro or something...

Richard H: Lukaku looks like he has already mentally checked out at Chelsea. Doesn't run, doesn't press, wants certain types of balls and complains if he doesn't get it and when he does get the service as he wants it and scored, he doesn't even celebrate.

Mason Mount whips in the corner and Thiago Silva heads it down but neither Romelu Lukaku nor Cesar Azpilicueta can turn it in before it bounces wide.

Boro keeper Joe Lumley flies out of his box to stop Christian Pulisic latching onto Hakim Ziyech's raking ball forward.

Boro need to just keep in this game.

Chelsea have a corner now.

Gary Rose
BBC Sport at Riverside Stadium

That was a great move from Chelsea. The Blues calmly played through Middlesbrough's high press and then turned defence into attack at such pace the hosts just couldn't get into shape in time.

The home fans had been in superb voice from the outset but now it is the pocket of away fans who are making themselves heard.

Romelu Lukaku has scored 16 FA Cup goals since his debut in January 2012.

Only Sergio Aguero (20) has scored more in that time.

Jermaine Jenas
MOTD2 pundit & former Tottenham midfielder on BBC One

This goal is absolutely brilliant.

Mason Mount has already made two or three of those runs and the quality of his cross produces a tap-in for Lukaku.

The delivery was just impeccable.