Man United 1 Midldesbrough 0:Gareth Southgate labelled Cristiano Ronaldo a "diver" earlier this season, and after winning another controversial penalty to take Manchester United into the semi-finals last night the Portuguese international could not resist the temptation to taunt Middlesbrough's manager.

Having scored the game's decisive goal, Ronaldo was quickly over to the visitors' dugout to signal to Southgate that he should have kept his counsel. Ronaldo, like Dr Bruce Banner, is clearly not a man to make angry.

His goal tees up a semi-final against Watford and keeps United on course for a potential treble of Premiership, FA Cup and Uefa Champions League.

Simultaneously, it will confirm Ronaldo's place as Middlesbrough's bete noire. Ronaldo, one suspects, enjoys the role of pantomime villain, but Carlos Queiroz, United's assistant manager, had to be restrained after objecting to some of the comments from the opposition bench and there were angry scenes after the final whistle.

James Morrison, the Middlesbrough substitute, took his retribution with a stoppage-time challenge, and video replays showed that Southgate was entitled to be upset and it was difficult not to sympathise with Middlesbrough, because until then they had frustrated their opponents with an outstanding defensive display.

Middlesbrough's intentions were made clear the first time Ronaldo collected the ball and three players in white shirts converged on him likes moths to a lamp. But Ronaldo is not a player who is easily discouraged by the presence of extra defenders.

Still, this was not a performance to match his demolition job of Bolton Wanderers two days earlier, and there were consequently spells when United were short of their usual fluency in attack.

For that, Middlesbrough's stoic defenders must take credit, although it was disappointing for the home supporters that Wayne Rooney took such a long time before working up a head of steam.

It was an untidy start, more notable for the number of misplaced passes than genuine scoring chances. Ronaldo flashed a venomous shot narrowly wide and, at the other end, Mark Viduka seemed to be under instructions to shoot at any opportunity, even from 40 yards on one occasion.

Yet, it was not until the 42nd minute that either side created a clear-cut opportunity, Ryan Giggs' exquisite pass sending Rooney bearing down on goal. Mark Schwarzer was quick to see the danger, charging off his line and sprawling himself over the ball as Rooney tried to dribble around him.

By that stage, Middlesbrough's attackers were looking increasingly isolated. All the play was on the edge of the visitors' penalty area, but, with Jonathan Woodgate and Emmanuel Pogatetz repelling Rooney and Smith, there was very little to generate excitement in a stadium showing unusually large expanses of empty red seats.

Woodgate, in particular, played as though he single-handedly wanted to justify Southgate's controversial decision to rest him from Saturday's defeat against Manchester City - until he conceded the penalty. It summed up United's frustrations in the first half that Smith resorted to scything down his former Leeds team-mate.

It was a very obvious booking and shortly afterwards Middlesbrough began to emerge as an attacking force. Viduka played in Downing for a chance he would conceivably have taken had it not fallen on his weaker right foot. Old Trafford was rattled.

Ronaldo came out of a relatively quiet period to strike the outside of the post. Then Woodgate challenged Ronaldo and the winger went to floor. His penalty was expertly taken and then the insults began.

MANCHESTER UTD: Kuszczak, Brown, Ferdinand, Vidic, Heinze, Ronaldo, Carrick, Giggs, Richardson (Park 60), Smith (O'Shea 71), Rooney. Subs not used: Heaton, Cathcart, Eagles. Booked: Smith, Rooney.

MIDDLESBROUGH: Schwarzer, Xavier, Woodgate, Pogatetz, Taylor (Huth 88), Cattermole (Morrison 62), Boateng, Arca (Rochemback 69), Downing, Yakubu, Viduka. Subs not used: Jones, Lee. Sent Off: Morrison (90). Booked: Xavier, Woodgate, Pogatetz, Boateng, Rochemback.

Referee: M Dean (Wirral).