Middlesbrough cruised into the FA Cup fourth round after a dominant second-half performance saw off League One side Peterborough at the Riverside.

Posh looked capable of a shock in the first half, and had a fine chance when striker Ivan Toney flashed over.

Boro punished the visitors after the break, through quick-fire goals from Britt Assombalonga and George Friend.

Lewis Wing thrashed in a third before Assombalonga's second and an Ashley Fletcher goal sealed a thumping win.

Only four Championship sides have scored fewer goals than Middlesbrough in the league this season and that lack of cutting edge looked like it might prove costly in a meek opening 45 minutes.

Peterborough contributed to an open first period, notably when Toney skied over the ball when one-on-one and Siriki Dembele drilled just wide.

Boro boss Tony Pulis tweaked his side at the break in response to a flat display, and it paid dividends as ex-Posh striker Assombalonga nodded in after Fletcher's shot struck the bar and Friend's second put the home side in control.

The introduction of academy products such as Wing, Stephen Walker and Harry Chapman was another boost, and they were prominent as Boro put the game out of sight with three goals in the final 20 minutes.

Middlesbrough boss Tony Pulis:

"The application of the players was very good. In the first half, we played with five forwards really with Tav (Marcus Tavernier) and Rajiv (van La Parra) out wide. They all pushed on, and if anything, I've made a mistake doing that because it blocked all the spaces we were really trying to use.

"Bringing [Lewis] Wingy on, and then pulling him and Grant (Leadbitter) out to play a bit more, sucked them on to us, and then there more spaces for us to play in.

"I think the big thing is we've scored five goals, and I'm really pleased with the attitude and application of the players. We played really well, especially second half. But we're playing against a League One side, we're not playing against a top Championship side."

On Ashley Fletcher's future:

"There's not just Hull that are interested, there are one or two other clubs as well. Will he stay here? We'll see what happens.

"It was great that he got his goal, but I thought he played well in the first half too. There were one or two who didn't do as well in the first half, and got better in the second half, but I thought Fletch was one of our better players in the first half as well. I'm really pleased with him."

Peterborough manager Steve Evans:

""I'll focus on the first 45, we gave them real problems and should have been two or three ahead at half-time. We missed some chances we'd have expected to take.

"You realise Tony is going to have a reaction in the dressing room, they changed the system but we have to defend properly.

"You've seen what's happened out there today. When they get the second and then the third it becomes a long day against such a talented squad.

"It's the best we've played in 10 months under me (in the first half). I thought we were terrific, made good chances, nullified their threat but you have to be capable of taking chances against any side in the Championship."