Two sides who endured very different starts to the new season, few would have expected such an open encounter at the London Stadium.
A game that somehow ended 0-0, both sides will still be ruing missed opportunities.
With West Ham picking up their first clean sheet of the season, they also ended Maurizio Sarri’s 100% start.
Although both sides left with a point, what did we learn from Sunday’s London derby?
1. The Hammers show their resolve
It’s amazing what can happen in a couple of weeks.
Losing their first four games of the season, the mood around the London Stadium was becoming increasingly sour.
However, putting three past Everton eight days ago, the increasingly good mood showed on the pitch on Sunday.
Gaining plenty of plaudits for his decision to play 4-1-4-1 on Merseyside, Pellegrini’s choice to tweak his formation to a 4-3-3 once again proved a smart move.
Not allowing some of Sarri’s more creative sparks to impact the game, West Ham were happy to let the Blues control the possession.
Compact and keen to catch their opponents on the counter, one man who epitomised the Hammers resolve was 19-year-old Declan Rice.
Taken off against Liverpool at half-time in their Premier League opener, the youngster has certainly bounced back.
Putting in a Man of the Match performance against Everton, Rice once again impressed in front of West Ham’s defence.
Making more interceptions than any player on the pitch, Pellegrini’s side look far more comfortable with a natural holding midfielder.
While Chelsea did have chances, it’s hard to argue that Pellegrini’s side didn’t contain the Blues for the best part.
2. Hazard is human
Sat top of the table prior to the weekend, there were whispers around Stamford Bridge that Chelsea could be a title dark horse.
However, much like last season, it appears they’re incredibly reliant on Eden Hazard to score the bulk of their goals.
Coming off the back of scoring a hat-trick against Cardiff, Sarri set the Belgian winger a 40-goal benchmark.
A number that raised a few eyebrows, all eyes were on the 27-year-old this weekend.
Although it might be becoming a rarity, Hazard was unable to muster up any of his usual magic.
Eden Hazard has never scored in four consecutive games across all competitions for Chelsea.
West Ham end his streak. pic.twitter.com/A7rdLjiwMq
— Squawka Football (@Squawka) September 23, 2018
On the two occasions that he did find himself with a sight at Fabianski’s goal, he unselfishly decided to try to find the misfiring Alvaro Morata.
If Sarri is serious about the winger picking up the Golden Boot, he will certainly be looking for him to be more selfish in similar opportunities.
Much like Tottenham need with Harry Kane, Chelsea could do with someone who can take the goalscoring burden off their talisman’s shoulders.
3. West Ham miss Arnautovic
Although the hosts would have bit your hand off for a point prior to kick off, some will feel they should have left with more.
With Marko Arnautovic sidelined with a thigh injury and with deputy Javier Hernandez fighting a virus, Michail Antonio was deployed as a makeshift number nine.
While the versatile Englishmen was an ever willing runner, he does lack that killer instinct.
Now failing to score in his last 27 appearances, the former Nottingham Forest man wasted two glorious chances in the first half.
It wasn’t just Antonio who couldn’t apply the finishing touch.
Undoubtedly the best opportunity of the game fell to last week’s two-goal hero Andriy Yarmolenko who couldn’t direct his free header from six yards.
Pellegrini and West Ham will know their top scorer wouldn’t have been so wasteful in front of Kepa’s goal.
Marko Arnautovic has scored 3 of @WestHamUtd’s 5 PL goals this season. He has been involved in 12 goals in his last 11 PL away apps (7 goals & 5 assists).
Has been Involved in 16 PL goals in 2018 (9 goals, 7 assists). Only Mohamed Salah has been involved in more PL goals (23) pic.twitter.com/MUF2dRLFGM
— Sky Sports Statto (@SkySportsStatto) September 16, 2018
Expected to make his return against Manchester United next week, there is no doubt that Arnautovic is the Hammers’ talisman.
The Austrian international is joint second for the most goal involvements in the Premier League in 2018 with 16.
He is level with Sergio Aguero, Eden Hazard, and Harry Kane.
4. A Europa League hangover?
While lifting a European title next May would equal a successful season, the demands of Europa League football can be a double-edged sword.
Playing on a Thursday night, often in some far corner of Europe, can have an effect on a squad, even a squad as big as Chelsea’s.
While squad rotation was expected, Sarri elected to play a surprisingly strong side for their opening match in Greece on Thursday night.
Their preparations were not helped by a delayed flight that saw them return in London just 48 hours beforehand.
With Rüdiger playing the whole 90 minutes against PAOK and then having to be taken off on Sunday with a muscle injury, questions were beginning to be asked.
Speaking to TalkSport, Sarri was quick to laugh off the Europa League being used an excuse for a poor performance.
“No, because we have played better in the second-half than the first-half. So in this period of the season, I don’t think so.
We knew today was a very difficult match. They are a very good team.
So I am not disappointed but I think we could have done better, especially in the last 25 minutes of the first-half. We played well in the second-half, very well in the last 25 minutes.
In the first-half we move the ball very slowly and there was little movement without the ball.”
5. Jorginho is the pass master
While West Ham may have put up a sterner test than what he was used to, Jorginho continues to show why he is an integral part of Sarri’s plans.
Playing under the Italian during Napoli’s rise, the 26-year-old has made an immediate impact in West London.
Attempting 180 passes on Sunday, no player in Premier League history has attempted more passes in 90 minutes.
Playing in almost a quarterback position in front of David Luiz and Antonio Rüdiger, Jorginho is the man who pulls Chelsea’s strings.
Also having 191 touches, he once again broke another Premier League record in just his sixth appearance.
Much like the impact N’Golo Kante had in his debut year, if the Blues are to mount a surprise title push, Jorginho could hold the key.
Had Willian not been so wasteful in extra time, the Italian would have picked up a contender for assist of the season.
Peach of a ball from Jorginho, but we have seen this from Willian far too much. pic.twitter.com/SWhpQkiPVF
— Alex Goldberg (@AlexGoldberg_) September 24, 2018
A master of keeping the possession, it’s no surprise Pep Guardiola was so desperate to take him to Manchester over the summer.