Mauricio Pochettino optimistic despite Chelsea loss against West Ham

The Blues were the better side but James Ward-Prowse, making his Hammers debut, created goals for Nayef Aguerd and Michail Antonio, either side of Carney Chukwuemeka's equaliser.

Enzo Fernandez had a penalty saved by Alphonse Areola and West Ham had to play the final 25 minutes a player down after Aguerd saw red.

Yet not only did David Moyes' side cling on for a first win of the season, they wrapped it up in stoppage time.

While Chelsea's £105million player missed a spot-kick, their £115million signing gave one away with Moises Caicedo, on as a substitute, sending Emerson Palmieri tumbling and Lucas Paqueta converting the spot-kick.

"I think today the result doesn't reflect the performance but in football these situations happen," said Pochettino.

"I am disappointed in the way we conceded the first goal. We know West Ham are good at set-pieces. That is a little bit disappointing and we need to work hard on that.

"Then I think also did really well in the first half and we should have been winning at half-time.

"But that is the process. We need to accept the defeat and keep on working.

"If we score the penalty we miss you are talking about a different game. We are going to perform better in the next games."

Ward-Prowse was brought in to replace Declan Rice in West Ham's midfield but he offers plenty more in attack.

His seventh-minute corner found Aguerd at the far post, and his clever ball over the top sent Antonio through on goal.

"His character is, in lots of ways, similar to Declan Rice," said manager Moyes.

"He's a really good boy. His delivery, his assists, that's what he's capable of and I thought he did a great job today. His corner gave us a great start."

Paqueta was in the West Ham line-up despite being reportedly investigated by the Football Association for potential betting rule breaches.

The Brazil midfielder is said to be shocked by the probe, which is believed to centre around bets placed in his homeland on yellow cards awarded against him.

A move to Manchester City may have fallen through so the 25-year-old celebrated his goal with the ˜crossed Hammers' sign.

"I thought 65,000 people stood to their feet and applauded him," added Moyes.

"He played as well as anybody, he showed character and his performance was very good, especially in the second half.

"There was never any doubt (he would play). He's a solid and tough character so no problems. He's a very good player."

READ MORE: Mikel Arteta downplays 'gamble' of having two top keepers at Arsenal