West Ham United's return to form continued as they beat Chelsea 2-0 in the fourth round of the EFL Cup.
This derby was billed as the biggest footballing test for the London Stadium so far, on a night when basketball and track cycling competitions were also taking place on the former Olympic Park.
Cheikhou Kouyate rose ahead of restored Chelsea captain John Terry to head the Hammers in front and Edimilson Fernandes struck a second three minutes after the interval.
The energetic and pacey Hammers exploited uncertainty in Chelsea's defence, with Terry making his first appearance in more than six weeks following an ankle injury.
A fifth victory from nine games at their new home saw the Hammers advance to the quarterfinals and remain in contention for silverware in their first season since leaving Upton Park.
Chelsea's only remaining cup competition this season is the FA Cup.
Joining Terry as one of seven Chelsea changes following Sunday's 4-0 win over Jose Mourinho's Manchester United was Asmir Begovic, who made his third League Cup appearance of the season in goal. Both appeared rusty.
Terry flicked over an early Willian corner, but otherwise struggled in the centre of Chelsea's back three.
And the 35-year-old was beaten to Mark Noble's cross by the onrushing Kouyate, whose header from the penalty spot soared past Begovic.
The impressive Michail Antonio shot narrowly wide before Nathaniel Chalobah's shot from 25 yards was tipped over at the other end.
Chelsea's N'Golo Kante next opted to cross when he might have been better to shoot and Manuel Lanzini should also have done better than prod Antonio's pass across goal.
An inswinging Dimitri Payet free kick was clawed away by Begovic, who next had to parry clear Pedro Obiang's shot from 30 yards.
Chelsea had chances, too. Michy Batshuayi had to stretch to meet Oscar's centre, firing well off target as the striker showed his lack of sharpness.
Chelsea were soon two down, despite switching the back three so Terry was on the left, Luiz in the centre and Cahill on the right.
Begovic saved well as Payet tried to turn in Antonio's cross and Kante only half cleared.
West Ham worked the ball right and Fernandes cut in on to his left foot before firing a shot through Terry's legs and into the bottom corner for his first Hammers goal.
West Ham had further chances before Conte sent on Diego Costa and Eden Hazard.
Costa tested the Hammers on numerous occasions, but Chelsea's only reply was Gary Cahill's late strike.