Antonio Conte's dismal London derby form continued as West Ham beat Chelsea 1-0 to hand David Moyes his first victory as Hammers boss.
Moyes' landmark victory was sealed by Marko Arnautovic, who fired his first goal for the club with just six minutes on the clock at the London Stadium.
Alvaro Morata and Eden Hazard spurned chances to rescue a point but the hosts clung on as Conte suffered his ninth league defeat at Chelsea - five of which have now come at the hands of London rivals.
West Ham remain in the relegation zone but a first win in nine gives them a timely boost ahead of the busy festive period.
Just as they did in last week's encouraging defeat at Manchester City, West Ham took the lead as Arnautovic played a one-two with Manuel Lanzini and slotted his first Hammers goal beyond Thibaut Courtois on six minutes.
Chelsea went on to dominate possession but had to wait until 29 minutes to register their first substantial attempts on goal as N'Golo Kante and Davide Zappacosta drew saves in quick succession from Adrian.
Conte wasted no time in changing his misfiring attack as Pedro, Victor Moses and Willian came on within 19 minutes of the restart.
But it was West Ham came close to finding the net as Arnautovic and the relentless Michail Antonio posed the greater threat on the counter.
A fatigued Hammers side dropped deeper and deeper as the game wore on, inviting pressure as Chelsea pushed for an equaliser.
But, having been played in by Kante, Morata fired a glorious chance wide on 84 minutes before Hazard shot over a minute later as the Blues failed to keep pace with the two Manchester clubs.
Opta stats
- Chelsea have already dropped 16 points in their 16 Premier League games this season - they only dropped 21 in the whole of 2016/17 season.
- This was David Moyes' first Premier League home victory as a manager in just under a year (December 17, 2016; Sunderland 1-0 Watford) and ended a run of 11 successive league home games without a win (W0 D5 L6).
- Marko Arnautovic became the 140th different player to score a Premier League goal (excl. own goals) for West Ham; only Spurs (142) have seen a higher number of players score for them in the competition.
- Arnautovic also became the 43rd different player to both score for and against West Ham in the Premier League; a higher tally than any other club in the competition.
- This was the 100th Premier League win that Mark Noble has played in for West Ham; the first player to reach this landmark for the club.
The managers
David Moyes: "The win was the biggest thing. To get a win in the Premier League is really hard especially against the champions. After that, I would say the spirit of the team, how they stuck together, their work-rate and their effort pleased me. The basics were, in the main, done well today."
Antonio Conte: "This is the fourth defeat in 16 games. In my previous experience, when you lose four games in a season, it's impossible to stay and fight for the title.
"In 16 games and to lose four, it means that a target must be another. If you want to stay in the race for the title in the first part of the season you can only lose once or twice."
The pundit
Jamie Redknapp: "They [West Ham] should be playing like this week in, week out. When you have a bench with people like Andy Carroll, Javier Hernandez and Diafra Sakho, it is a bench that teams at the bottom of the league would love to have.
"Now they have to adhere to this every week because some of the performances haven't been good enough. To be on 10 points before today with that group of players and performing like that against Chelsea, they have to do this week in, week out."
Man of the Match - Marko Arnautovic
Arnautovic looks unrecognisable compared to the player that was operating under former boss Slaven Bilic earlier this season, and showed his class as his superb maiden goal for the club clinched victory against the champions.
What's next?
It's a second London derby on the spin for West Ham as they host Arsenal at the London Stadium on Wednesday. Before that, Chelsea travel north to take on Huddersfield on Tuesday.