Chelsea suffered a 3-1 defeat as they took on West Ham United in the Premier League at the London Stadium on Sunday evening.
The hosts got off to a lightning quick start, after just seven minutes, former Southampton star and recent summer signing, James Ward-Prowse, spun a corner onto the head of Nayef Aguerd who guided his effort past Robert Sanchez and into the net.
While it was not how Chelsea wanted the game to get underway, they responded well, midway through the first half, Carney Chukwuemeka managed to find some space in the box and levelled the match with a thumping effort.
Before the half-time interval, the Blues should have had the lead, Raheem Sterling was tripped in the penalty area by Tomas Soucek and a spot-kick was awarded, Enzo Fernandez stepped up to take but the Argentine was denied by Alphonse Areola and the teams went into the break level.
Despite Chelsea looking the stronger of the two sides in the opening 45, in the second half they quickly found themselves behind again, a sharp counter-attack saw Michail Antonio fire home from distance.
Things were not looking good for the away side, but the door was opened for a potential comeback when Aguerd was sent off for a second yellow after a poor tackle on Nicolas Jackson.
The Blues were unable to create anything clear cut in the closing moments and it was instead the hosts who added to their lead when Lucas Paqueta converted a 94th minute penalty.
Pochettino made just one change to his side after being held to a 1-1 draw last weekend against Liverpool, Reece James, who picked up a hamstring injury, was replaced by Malo Gusto who earned his first start in a competitive game for the Blues.
It was a disastrous beginning to the game for the visitors, a curling delivery from West Ham debutant Ward-Prowse picked out Moroccan defender Aguerd at the back post, he nodded home to give the Hammers an early lead.
Chelsea looked to fire back quickly, Jackson darted in behind the defence and the Senegalese forward was brought down by Areola, while referee John Brooks had pointed to the spot initially he changed his decision immediately after noticing the offside flag was raised.
The west Londoners did manage to start to get more of a hold on the game as it progressed, chances came from Jackson, Sterling and Conor Gallagher, but it was 19-year-old Chukwuemeka who tied the contest in the 28th minute.
It was a wonderful goal from the youngster, his first ever in a Chelsea shirt, he elegantly cut inside onto his right foot and powered his strike past a helpless Areola to get the Blues back level.
As the opening 45 drew to a close, the visitors really should have taken the lead, a penalty was awarded when Soucek brought down Sterling in the box, but Fernandez squandered the opportunity from the spot and was denied by Areola.
Moments afterwards, another chance fell to the Blues, a burst of pace from Sterling saw him dart past the West Ham defenders, his cross was missed by both Jackson and Chukwuemeka and Chilwell could only manage a tame effort that was comfortably cleared.
Having missed chances, Chelsea only went into the half-time break level with the Hammers.
There was some unfortunate news to start the second half for the Blues, after limping off before the break, it was confirmed that goal scorer, Chukwuemeka, would play no further role in this contest, he was replaced by Mykhailo Mudryk during the interval.
Once again, Chelsea were slow out the gates, after Axel Disasi gave away possession, Ward-Prowse picked out Antonio who held shrugged off Levi Colwill and blasted Moyes’ team back into the lead.
As the Blues looked to fight their way back into this contest for the second time, Pochettino decided to introduce £115 million man, Moises Caicedo, with Ben Chilwell coming off.
As the second half reached the midway point, things were beginning to look a bit dire for the Blues, but they were handed an opportunity, a clumsy, late challenge from Aguerd, who had picked up a yellow card already in the first half, saw him receive his marching orders.
Chelsea looked to craft opportunities against the low block West Ham held as the final whistle drew closer, substitute Noni Madueke went closest, his deflected effort looked as though it may creep in, but Areola was able to tip it around the post.
It was already bad enough for the visitors, but in the closing moments of added time, a clumsy challenge from Caicedo handed the Hammers a penalty which Lucas Paqueta converted to wrap up the contest.
The Blues went close, but failed to come away with even a point from this game. They have now won just once in their last 14 games.