Match ends, Liverpool 0, West Ham United 0.
An inexperienced Liverpool side were frustrated by West Ham goalkeeper Darren Randolph as their FA Cup fourth-round tie ended in a goalless draw.
The Hammers had early chances but an unmarked Enner Valencia misjudged a header and Pedro Obiang volleyed wide.
Randolph twice blocked powerful Joao Teixeira efforts and also saved shots from Cameron Brannagan, Joe Allen and Christian Benteke.
But neither side could score and they will meet again in a replay in London.
The worst possible result for Liverpool?
Liverpool boss Jurgen Klopp played a youthful side in the third-round match and subsequent replay against Exeter, but included a mixture of first-team players and youngsters for the visit of the Hammers.
Goalkeeper Simon Mignolet, 27, was the oldest player in the Reds' starting line-up, which also included four players - Brad Smith, Cameron Brannagan, Kevin Stewart and Joao Teixeira - who had never started a Premier League match.
This was the ninth game that Liverpool had played in January, and they desperately did not want another match, but that is exactly what they got.
It means their schedule in February will now include at least seven matches, including the League Cup final, two Europa League matches, three Premier League games and one, maybe two, FA Cup ties.
Nevertheless, Klopp will feel his side should have won. A poor touch when only six yards out to waste a chance summed up another ineffective performance from an out-of-form Christian Benteke.
Liverpool were the better team in the second half and created numerous chances, but stand-in captain Allen shot harmlessly over, and Brannagan, Teixeira and Benteke had shots saved by Randolph.
How did Liverpool's youngsters do?
Generally, they were very impressive. Brannagan, 19, who consistently impressed with his set-piece delivery, nearly opened the scoring with a powerful shot from 20 yards out, but goalkeeper Randolph did well to push the ball around the post.
Brad Smith, 21, produced an energetic performance at left-back, often getting forward to help his side's attacks, while handling the threat from the quick Victor Moses with maturity.
Kevin Stewart, 22, a tough-tackling central midfielder, worked hard, making six tackles and two interceptions, and 23-year-old Joao Teixeira, playing on the left side of Liverpool's front three, was twice denied by a diving Randolph.
A wasted opportunity for West Ham?
Three-time winners West Ham were aiming to reach the fifth round of the FA Cup for the fourth time in the last eight seasons - and will have been buoyed when they saw the Liverpool line-up.
They themselves made five changes, although fielded a team rich in Premier League experience apart from Randolph, who played because regular goalkeeper Adrian was back in his native Spain for family reasons.
Yet the Hammers could not take full advantage. They kept trying to utilise Victor Moses' pace against Brad Smith down the right wing, but the defender often came out on top before Moses was withdrawn midway through the second half.
Slaven Bilic will argue that West Ham should have had a penalty, when Steven Caulker appeared to handle in the penalty area, but the Hammers took 50 minutes to have their solitary shot on target.
Man of the Match - Darren Randolph (West Ham)
What the managers said
Liverpool manager Jurgen Klopp said: "We had the bigger chances, but now we have to play again. West Ham have good quality in their team and play well in the league. We tried everything - you need a bit of luck.
"I was pleased with the whole team. Steven Caulker played for the first time in his position in defence and did well, but I cannot fault anyone, they tried and gave all. We played much better than we did at West Ham [in the league], but we didn't score so it is not over.
"The players we changed had the day off today so hopefully nothing happened to them."
West Ham boss Slaven Bilic said: "They had a few moments, we had a few moments. They were better in the second half - they could run more and were better at winning the second balls so it is a great result for us.
"We lacked that kind of quality we normally have in the last third of the pitch, so overall I am happy with the result.
"When you make two subs in the first half your hands are tied in the second half. It limited our options and we had to wait to make a third substitution. Kouyate should be OK for Tuesday hopefully."
Asked if they should have had a penalty for a Steven Caulker handball, Bilic said: "I didn't see the replays so I can't comment. I shouted a few times, they shouted a few times, the crowd shouted a few times, but that is part of the game."
The stats you need to know
- Liverpool have now not lost in their last seven FA Cup meetings with the Hammers (won four, drew three).
- The Hammers have won just one of their last nine FA Cup games away from home (drew two, lost six).
- In all competitions, West Ham United have won just two of their last 11 away matches (won two, drew five, lost four).
Both teams are next in Premier League action on Tuesday. Liverpool travel to Premier League leaders Leicester City, while West Ham welcome the division's bottom team Aston Villa to Upton Park.
- 6LovrenBooked at 54mins
- 44B Smith
- 32BrannaganSubstituted forSinclairat 86'minutes
- 33IbeSubstituted forOjoat 80'minutes
- 53Vilaca TeixeiraSubstituted forEnrique Sanchez Diazat 90'minutes
- 3Enrique Sanchez Diaz
- 5TomkinsSubstituted forO'Brienat 35'minutes
- 8KouyatéSubstituted forJelavicat 37'minutes
- 20MosesSubstituted forAntonioat 70'minutes
- 11E Valencia
- Martin Atkinson
- Shots on Target
Second Half ends, Liverpool 0, West Ham United 0.
José Enrique (Liverpool) wins a free kick in the defensive half.
Foul by Michail Antonio (West Ham United).
Foul by Christian Benteke (Liverpool).
Angelo Ogbonna (West Ham United) wins a free kick in the defensive half.
Substitution, Liverpool. José Enrique replaces João Teixeira.
Brad Smith (Liverpool) wins a free kick in the attacking half.
Foul by Pedro Obiang (West Ham United).
Jerome Sinclair (Liverpool) wins a free kick in the defensive half.
Foul by Pedro Obiang (West Ham United).
Corner, West Ham United. Conceded by Steven Caulker.
Attempt blocked. Michail Antonio (West Ham United) right footed shot from the centre of the box is blocked. Assisted by Dimitri Payet.
Substitution, Liverpool. Jerome Sinclair replaces Cameron Brannagan.
Attempt missed. Kevin Stewart (Liverpool) right footed shot from the left side of the box is high and wide to the right following a set piece situation.
João Teixeira (Liverpool) wins a free kick in the attacking half.
Foul by Winston Reid (West Ham United).
Attempt missed. Joey O'Brien (West Ham United) right footed shot from outside the box misses to the right. Assisted by Dimitri Payet.
Delay over. They are ready to continue.
Delay in match João Teixeira (Liverpool) because of an injury.