Striker Andy Liddell continued his love affair with this season's FA Cup to fire 10-man Sheffield United into a fifth-round showdown with Arsenal.

Liddell scored the decisive penalty to end a spot-kick shoot-out with West Ham, during which Blades goalkeeper Paddy Kenny saved from Teddy Sheringham and Marlon Harewood.

It was Liddell who opened the scoring in the eighth minute, only for Sheringham to net West Ham's equaliser 17 minutes into the second half, ironically from the spot after skipper Chris Morgan had been sent off for a second bookable offence.

The home side then played for 58 minutes with 10 men, and it was manager Neil Warnock's side who held their nerve to go through to the last 16 for the third successive season and set up a repeat of the semi-final clash with the Gunners in 2003.

In fairness, Warnock's side should have had the match won by half-time, with their failure to do so perhaps signifying their recent slump as they came into the game on the back of a four-match winless streak.

But they made the ideal start, taking an eighth-minute lead courtesy of a rasping free-kick from Liddell, whose two goals helped send Aston Villa packing in the third round.

Carl Fletcher's shove on Paul Shaw just outside the area gave Liddell a sight of goal, and he made no mistake with a 20-yard right-foot shot round the wall and beyond the grasp of Stephen Bywater.

Following that, though, chances came and went, with Bywater sparing the blushes of his captain Malky Mackay in the 20th minute as a weak back-pass header was intercepted by Andy Gray who then saw his attempted chip plucked out of the air by the 24-year-old goalkeeper.

When a Sheringham free-kick was comfortably dealt with by the home defence, it sparked a rapid counter with Phil Jagielka playing a one-two with Michael Tonge.

The West Ham defence was stretched, but an attempted return from Jagielka into the path of Tonge inside the area was cleared by Anton Ferdinand, who saved his side again shortly after with a block in the six-yard box to a shot on the turn from Gray.

A ricocheted shot just over the bar from Sheringham off Jon Harley was as close as the visitors came to finding the equaliser in the first half, with the Blades maintaining the pressure following the interval.

Bywater was forced into two fine saves to keep Warnock's side at bay, firstly beating away Tonge's angled shot and then likewise to a snap effort from Gray.

In between, Sheringham was inches over the bar with a 30-yard free-kick curler after Morgan had brought down Harewood in the 52nd minute.

That brought about a booking from referee Mark Clattenburg, who just nine minutes later was issuing a second yellow card and subsequent red to Morgan for a clumsy challenge on the Hammers forward inside the area.

As last man, Morgan was rightly sent off, but more importantly it allowed Sheringham to step forward and stroke home the penalty for his 12th goal this season, sending Kenny the wrong way from the spot.

Although the complexion of the game had changed, Hammers' spirits were only temporarily revived because after Kenny had made his first meaningful save in beating away a fiercely-struck Harewood drive soon after, it was the Blades who ended the 90 minutes the stronger.

Despite a man down, the home side dominated the first period of extra time, yet failed to create anything clear cut.

In a more even second period it was the Hammers who had the best chance to win the game and spare the angst of penalties, with Fletcher curling a far-post cross from the right wing where an unmarked Hayden Mullins planted a free header narrowly over the bar.

But penalties followed and Gray, Harley and Liddell were all on target, with Tonge and Jagielka missing high and wide respectively. After Kenny's heroics to save the first two spot-kicks, Mark Noble scored the visitors' only 12-yarder as Fletcher also blazed over.