Newcastle produced a powerful second-half display to book their place in the FA Cup fifth round for the third successive season.

The home side went in front with just five minutes gone as Alan Shearer fired home his 19th goal of the season.

But hopes of a shock were back on track 12 minutes later when former Sunderland midfielder Martin Smith got the visitors into it again.

Bobby Robson's side were again not at their best before the break, with Marcus Bent causing problems and Rob Lee's absence painfully apparent.

But once Gary Speed took on the holding duties in the centre of the park the fluency returned.

Nikos Dabizas put the Magpies 2-1 up two minutes after the break and further goals from Duncan Ferguson and Kevin Gallacher - his first for the club - made it safe.

Newcastle were indebted to Peruvian midfielder Nolberto Solano, whose service to the front men was exemplary on a day when brave defence was not enough.

Newcastle made just one change to the side which drew 2-2 with West Ham on Monday, with England midfielder Kieron Dyer replacing the injured Lee.

Sheffield United were without loan signings Paul Hall and Michael Brown, the suspended Shaun Murphy and hamstring victim Paul Devlin, but Wayne Quinn passed a late fitness test on a shoulder injury to take his place in the line-up.

Newcastle could have been in front with just 20 seconds gone when Ferguson nodded back Dyer's cross and Shearer sent a header over.

But the England skipper made amends in the fifth minute when he timed his run to perfection to slam Solano's corner past Simon Tracey from close range.

However, the danger signs were there from the off as Blades striker Bent made life uncomfortable for Dabizas and Marcelino, and keeper Steve Harper earned his corn with a good block from midfielder Shaun Derry escaped from Speed and Marcelino and raced into the box.

Shearer should have increased his side's lead on 16 minutes when Dyer laid the ball back to him on a plate, but he shot high over - and the First Division side made the most of their escape within a minute.

Jonathan Hunt delivered a cross to the far post where Smith ghosted past the sleeping cover to beat Harper from close range.

Newcastle were never allowed to settle and although the Blades defence looked shaky at times there were few scares for Tracey as the half wore on.

Ferguson sent a 39th-minute header just wide from a another Solano corner, but in truth, chances were few and far between in an increasingly even affair.

It took the Magpies just two minutes of the second half to get their noses back in front as the visitors' defence could only partially block Speed's header from Solano's corner and Dabizas ploughed in to bundle the ball home.

The setback seemed to take the wind out of the First Division side's sails and Ferguson had already had a header saved when he cashed in on Alessandro Pistone's excellent run to crash home a right-foot shot to make it 3-1 on 59 minutes.

Newcastle's play became more relaxed as they made the most of their blossoming domination and Gallacher produced a powerful finish after running on to Shearer's knock down 10 minutes later to collect his first goal for the club since moving from Blackburn.

Speed thought he had made it five nine minutes from time after an exhilarating run from Dyer, but an offside flag brought a disappointing end to his celebrations.

Robson's side were in complete control as the minutes ticked away but the Blades battled manfully to reduce the deficit and England Under-21 international Curtis Woodhouse almost ended his afternoon in style when he hammered an injury-time volley just over Harper's bar.

But the final whistle sent Newcastle back on the road to Wembley with renewed hope of a third successive appearance in the final.

Teams:

>Newcastle: Harper, Barton, Marcelino, Dabizas, Pistone (Domi 82), Solano, Dyer (Fumaca 86), Speed, Gallacher (Ketsbaia 82), Shearer, Ferguson.

Subs Not Used: Given, Hughes.

Booked: Speed, Shearer.

Goals: Shearer 5, Dabizas 47, Ferguson 59, Gallacher 69.

Sheff Utd: Tracey, Kozluk, Gybreches, Sandford, Quinn (Ribeiro 65), Derry (Hamilton 82), Woodhouse, Ford, Hunt, Bent (Katchouro 82), Smith.

Subs Not Used: Smeets, Doane.

Booked: Sandford.

Goals: Smith 17.

Att: 36,220

Ref: M Halsey (Welwyn Garden City).