Manuel Pellegrini took full responsibility after West Ham crashed out of the Carabao Cup following this humbling at Oxford. The League One side scored four unanswered goals via Elliott Moore, Matty Taylor, Tariqe Fosu and the excellent Shandon Baptiste to progress into the fourth round for the first time in 22 years.

West Ham had made nine changes after the 2-0 win at home to Manchester United in the Premier League on Sunday and Pellegrini said: “The whole team didn’t play well.

“Not only did we concede four goals, but we didn’t create too many chances. We missed too many passes from the beginning and the responsibility is first on me because I picked the players and second of course on the team that didn’t compete.

“We talked enough with all of them to understand that the competition was different, the team was different and to play now against Oxford, who were in a good moment after winning 6-0 [at Lincoln] in their last game.

“The players must understand, but I repeat we couldn’t do it because in front was a team that played very well. I don’t want to take anything away from Oxford because they played very well.”

Only Issa Diop and Pablo Fornals retained their starting berths from the win over United, but Pellegrini introduced Felipe Anderson and Sébastien Haller off the bench early in the second half. He defended his team selection here, insisting it was a necessity because of their fixture schedule.

He said: “I think in England if you want to play in all the competitions you need to use your whole squad. You cannot just continue with the same players that play on Saturday.”

West Ham supporters were making plenty of noise during the opening exchanges, including mocking their London rivals Tottenham, who were dumped out of the competition on penalties at Colchester on Tuesday. But Oxford delivered a brutal shock to send another Premier League side out.

Pellegrini’s counterpart, Karl Robinson, was delighted with his players and urged the 9,000 home supporters to turn up again for Saturday’s league fixture with Gillingham. “We had the belief in ourselves that we could get a result,” he said.

“I’m over the moon for the fans and the players. It’s about the players, about the fans and about the community of Oxfordshire and the big thing for me now is the people who came here for the first time in a long time, that they buy a ticket and come on Saturday. We want them to support us moving forward because economical growth is important for what we are trying to achieve.”

Robinson, who masterminded a 4-0 win against Manchester United five years ago as MK Dons manager, admitted the result was one of Oxford’s best at home in recent years, surpassing their FA Cup wins against Newcastle and Swansea.

“Looking at the scoreboard, 4-0 against West Ham and a very strong West Ham, this will probably go down as one of the biggest results at the Kassam in recent years.”

Robinson’s side quickly got back into their stride after the substitution and hit the crossbar with when Hall’s free kick almost crept in.

West Ham responded with the lively Holland testing Simon Eastwood from a tight angle on the left before Moore cleared the loose ball. Jack Wilshere tried his luck from range in the 32nd minute, yet it was a comfortable for the U’s goalkeeper.

Robert Snodgrass was denied a shot on goal by Rob Dickie early in the second period before the hosts’ confidence increased again when Roberto sliced a clearance behind for a corner.

West Ham survived that set piece and the next, but Robinson’s team kept the ball alive and Mark Sykes crossed in for Moore, who controlled and fired into the bottom corner from eight yards. shock was firmly on the cards and Sykes was giving Arthur Masuaku plenty of problems and almost created a second for Oxford two minutes later when Mackie flicked goalwards, but Roberto produced a brilliant stop to save the Hammers. It was one-way traffic, with the U’s eager for a second and Pellegrini reacted by introducing Sebastien Haller and Felipe Anderson, but it failed to have the desired effect.

Oxford increased their lead with 19 minutes left. Sykes was allowed too much space on the right and he crossed in for Taylor to tap home at the back post. Fosu, fresh from a hat-trick at Lincoln on Saturday, then slipped past Arthur Masuaku, rounded Roberto and slotted home. In added time Baptiste side-footed into the bottom corner to send Oxford into the fourth round, and with it a home tie against Sunderland, for the first time since 1997.