A clearly upset Boro manager labelled the Portuguese international a serial diver for the way he helped to break the deadlock by going to ground to earn a crucial first-half penalty.

Louis Saha banished the memory of his Champions League spot kick miss at Celtic to bury his 10th goal of the season, paving the way to a victory that increased the leaders' advantage over second-placed Chelsea to a commanding six points.

Ronaldo made the most of an innocuous first-half challenge with Boro's Australian international keeper Mark Schwarzer, as replays revealed minimal contact, and Southgate said: "The man's cheated on the night, it's as simple as that.

"It's very difficult for the referee, because it happens very quickly and I can't blame him, but how many times are we going to see it?

"The lad's got a history of doing it, and in the end it's cost us the game because it gave us a mountain to climb. There's clearly no contact whatsoever, the keeper's done everything to get out of the way and the lad goes down once again, there's a history of it. It's never a penalty.

"I don't know what you do to stamp it out, and it happened again in the game after that for a free-kick. It's for people who are better qualified than me to deal with."

Southgate could barely bring himself to discuss Ronaldo's pivotal role, such was his annoyance, and he added: "To be honest, I'm not interested in talking about him. He plays the way he obviously thinks is the right way and that's fine.

"You'd hope some players would perform in a manner they should do and when they've got a chance to stay on their feet they don't try to look for a penalty."

Alex Ferguson insisted the 19th-minute clash merited a penalty, although the Manchester United manager admitted his sympathy for referee Chris Foy. He said: "It was hard for the referee but of course it was a clear cut penalty.

"It looks as though the keeper hasn't touched him, but there was clearly intent. What's Cristiano going to do? He was going to get carted anyway."

Southgate, who revealed defender Jonathan Woodgate should be fit to face Tottenham Hotspur on Tuesday after being forced off at half-time through illness, believes United can hold-off Chelsea to end the London club's two-season title domination. "United are an excellent side," he added.

Only a fine Schwarzer display kept Boro in the hunt following Saha's confident penalty, as United dominated en route to a ninth victory in their last 10 league games.

Despite Abel Xavier hitting the post with a first-half header, it came as a surprise when the hosts equalised through substitute James Morrison's angled second-half volley, as Argentine defender Gabriel Heinze failed to clear Stewart Downing's cross.

United were ahead again within two minutes thanks to Darren Fletcher's second goal of the season, a close range header from Ryan Giggs' centre, as Boro fell to a classic sucker punch to cut their celebrations short.

Ferguson added: "This was a very important result for us. The lads showed a great deal of character and resolve to bounce back after Middlesbrough equalised.

"As we know from past experience this is a difficult place to play, but our form's fantastic, which it needs to be with things being so tight with ourselves and Chelsea. We're showing the consistency you need to win championships and if we maintain it then we've got a great chance."