Liverpool won the grudge match but the Kop lost its reputation for sporting behaviour yesterday, when Alan Smith was removed from this fifth round FA Cup tie on a stretcher to choruses of “Hey, Arne Riise, I wanna know how you broke his leg.”

Liverpool fans have adopted the old Bruce Chanel song, Hey Baby, to salute goals scored by their Norwegian favourite, John Arne Riise. On this occasion, however, it was used to taunt the opposition after Smith had sustained a fractured left leg and dislocated ankle in the act of blocking Riise’s 89th-minute free kick.

What Sir Alex Ferguson described as “the worst injury I’ve ever seen” was a sickening finale to a fractious afternoon of seven bookings when legitimate competitiveness threatened to give way to something unacceptable. There is real enmity between these two teams and their fans, and passions had been inflamed by the corresponding fixture in the league at Old Trafford last month, when United scored a last-minute winner and their captain, Gary Neville, overdid his celebrations in front of the Liverpool supporters, for which he was charged with incitement by the Football Association.

Harry Kewell and Fernando Morientes, among others, had fanned the flames by saying that scores were going to be settled, with revenge the order of the day, and it was apparent throughout that Liverpool were as “up for it” as it is possible to get. Immediately before the kick-off, their supporters launched into You’ll Never Walk Alone with a volume intended to intimidate, and Neville was booed every time he was in contact with the ball.

The full-back, celebrating his 31st birthday yesterday, has brought much of this unpopularity upon himself, but nobody should have to endure obscene abuse, in this case about his mother, that United players seem to attract — witness David and Victoria Beckham.

For the Liverpool players and their manager, Rafael Benitez, it was a shame that this horrific threat to poor Smith’s career should overshadow an impressive professional performance.

Incredibly, it was 1898 when Liverpool last beat their great rivals at Anfield in the FA Cup, and they went about their work here like men on a mission.

The match was won and lost in midfield, where Ryan Giggs and Darren Fletcher were lightweight and easy meat for Steven Gerrard and Dietmar Hamann.

United were second best. Jose Reina was not called upon for a single save worthy of the name. The nearest they came to scoring was in the 80th minute, when Ryan Giggs was not far away with a volley from the edge of the D. That said, Liverpool, for all their possession, were only marginally better in terms of decent goal attempts. They were effective, rather than pretty, which has usually been the way of it under Benitez.

Ferguson approached the tie in the erroneous belief that attack was the best form of defence, loading his team with forwards and stationing Giggs in the centre of midfield. Liverpool could not believe their luck, and seized an initiative they were never to lose.

Kewell, taking advantage of a flaky start by Neville, which suggested he had been unnerved by his reception, had already threatened with a dangerous cross, when his second contribution of note, after 18 minutes, led to the only goal. The Australian is back to form after a dip of Turin downhill proportions, and the header with which he met Gerrard’s free kick had Edwin van der Sar flying across to turn the ball behind. Gerrard sent the corner short to Steve Finnan, whose centre was headed in by Peter Crouch eight yards out. Van der Sar, at full stretch, got a hand to the ball, but could only help it in via his left-hand post.

Nemanja Vidic, United’s new centre-half, was culpable, letting Crouch get away from him. It was the first goal scored by a Liverpool striker in 2006, which was not as surprising as it should be. Morientes is football’s equivalent of bird flu — lethal on the Continent, but yet to do damage in this country.

Yet Liverpool should have increased their lead. Finnan shot wastefully from another Gerrard free kick, then Crouch failed to profit from a mix-up between Vidic and Van der Sar, prodding the ball wide.

Plan A having gone horribly wrong, Ferguson used the interval to change his formation, sending on Louis Saha for Mikael Silvestre and switching from 4-3-3 to 4-4-2. This brought about an improvement of sorts, but at no stage were United able to string together enough passes. On the contrary, they gave the ball away with bewildering regularity.

The terrible injury came with only a minute of normal time remaining. Smith, nothing if not brave, threw himself at Riise’s free kick, which he succeeded in blocking, only for his leg to collapse under him.

He won’t be going to the World Cup. The football fraternity, with the exception of those morons on the Kop, will wish him a speedy and successful recovery.

STAR MAN: Dietmar Hamann (Liverpool)

Player ratings. Liverpool: Reina 6, Finnan 7, Carragher 7, Hyypia 8, Riise 7, Gerrard 7, Hamann 8, Sissoko 7, Kewell 7 (Kromkamp 82min, 6), Crouch 7 (Cisse 88min, 6), Morientes 6 (Luis Garcia 62min, 6)

Manchester United: Van der Sar 5, Neville 6, Brown 6, Vidic 5, Silvestre 5 (Saha h-t, 5), Ronaldo 6, Fletcher 4 (Smith 76min 5, Park 90min, 5), Giggs 5, Richardson 5, Rooney 5, Van Nistelrooy 5

Scorer: Liverpool: Crouch 19

Referee: H Webb

Attendance: 44,039

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