LONDON -- Liverpool's 3-2 defeat at West Ham came as a surprise given they were the Premier League's last unbeaten team, but there was a moment midway through the second half when manager Jurgen Klopp knew it was coming.

With the game delicately poised at 1-1, play came to a standstill close to his technical area just after the hour mark and the Liverpool boss' agitation was palpable with a team that looked ragged and was losing shape, while trying to force the issue having dominated possession.

Klopp shouted at right-back Trent Alexander-Arnold, instructing him to stay closer to the flank rather than drift infield. The manager circled the air with his hands, desperately telling his players to resume playing in a more controlled manner.

He readied substitute Thiago Alcantara to help them do just that, but before the Spanish midfielder could come on, West Ham retook the lead. Sadio Mane lost possession and Liverpool were exposed. Jarrod Bowen burst forward and timed his pass to perfection, releasing Pablo Fornals for a low shot that Alisson should arguably have saved.

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These are heady days for David Moyes and West Ham. In the euphoria that followed, Liverpool lost their composure and Kurt Zouma added a third with a far-post header from Bowen's corner. Divock Origi halved the deficit, but the Hammers held on for a deserved win.

Although the result sees them drop to fourth -- leapfrogged by Sunday's opponents -- the recriminations shouldn't be too brutal for Liverpool. After all, they had not lost for 25 matches across all competitions and sit just four points behind leaders Chelsea and one adrift of Manchester City.

But the Hammers were supposed to be the team struggling to cope with the additional demands of European football, not a Liverpool side that wore the effects of a draining week, which began with a 2-2 draw against Brighton before an authoritative 2-0 Champions League win over Atletico Madrid.

"We should have controlled the game still in the second half and for whatever reason, it looked a little bit for me like we lost patience," Klopp said. "We didn't have enough clear-cut chances, so we wanted to change the wrong things. Our passing changed too early. We had to do it higher up the pitch as then you are better protected, but we were in situations where we lost the balls."

Perhaps that second-half slump suggests injuries are starting to catch up with the Anfield club. Up front, Diogo Jota struggled to offset Roberto Firmino's absence, but the issue is more prevalent in midfield.

This was Fabinho's second start in five days after missing the last five games with a knee problem. Meanwhile, with Naby Keita (hamstring) joining James Milner, Curtis Jones and Harvey Elliott on the sideline, Alex Oxlade-Chamberlain has not convinced he can pin down the central midfield role he has long coveted.

Thiago only returned from six weeks out with a calf injury as a substitute against Atletico and has been inevitably rusty. As such, the decision by Liverpool not to replace Georginio Wijnaldum, who left as a free agent after last season, feels particularly relevant on days like this.

And yet, what came before and after West Ham's quick double strike, which proved the defining passage of the game, threatened to deliver a different outcome.

West Ham took a fourth-minute lead when Angelo Ogbonna's challenge on Alisson from Fornals' corner survived a lengthy VAR check, first for a foul and then handball. Under pressure from Ogbonna, Liverpool's goalkeeper got the final touch as he fell backward, diverting the ball into his own net via the far post.

"It is a clear foul on Alisson," Klopp said. "How can it not be? The arm from Ogbonna is there. You always have to say the ref (Craig Pawson) maybe in the game can see it but when you see the dynamic of the whole situation, when they all go down, how close they are.

"They are in each other, how can that not be a foul already without pushing the arm of Alisson? But the ref made it easy for himself and thought 'come on, let's see what the VAR is saying.' VAR [Stuart Attwell] had a look and said 'not clear and obvious,' and gives the goal which is really strange."

Liverpool's response was impressive. After Aaron Cresswell survived another VAR check for a high tackle on Jordan Henderson -- described by Klopp as a "reckless challenge" worthy of a "clear red card" -- the visitors began to monopolise possession, albeit without initially testing goalkeeper Lukasz Fabianski.

That changed four minutes before the break. Mohamed Salah went down rather easily under a challenge from Cresswell and, after shifting the ball right and a touch from Salah, Alexander-Arnold delivered a pinpoint free kick that curled inside the left-hand post and left Fabianski rooted to the spot.

And after Fornals and Zouma turned the game in West Ham's favour, Liverpool rallied again. Alexander-Arnold's persistence led to a loose ball that substitute Divock Origi volleyed home after a superb turn; it was Alexander-Arnold's 46th Premier League goal involvement (nine goals, 37 assists), surpassing John Arne Riise as the most by any Liverpool defender.

Two more superb deliveries gave Liverpool chances to snatch a point, but Mane headed wide from six yards, then Origi could only head tamely at Fabianski.

After his 1,001st match as a manager, Moyes revelled in celebrations that were witnessed by Czech businessman Daniel Kretinsky. He remains in talks to buy a stake in West Ham -- the price may have gone up a little after this result -- while Klopp focused his frustration on Pawson.

With the international break upon us, Liverpool's leader has plenty of time to calm himself. More significantly, ahead of a clash with Arsenal on Nov. 20, he has two weeks to get players fit again. Sunday proved how important that could be.