LONDON -- Three points from the London Stadium as West Ham held Chelsea to a 0-0 draw to end the Blues' 100 percent start to the season.
1. Chelsea toothless, resurgent West Ham spirited but missing Arnautovic
Chelsea's flawless Premier League start had come as a surprise, not least because of Sarri's admission in August that he expected "problems" in the first half of the campaign. Problems arrived against West Ham, and in the end a draw was the fairest outcome between two teams undermined by mistakes at both ends.
Pedro was Chelsea's only significant absentee, thanks to the shoulder injury he picked up in the final seconds of the midweek win over PAOK, but he was missed. Eden Hazard and Willian were both stifled for much of the afternoon and, even when they found space, their own bad decisions proved their undoing.
Willian in particular showed little chemistry with N'Golo Kante on the right flank, as Chelsea's bright start gradually devolved into sterile possession in the face of West Ham's stubborn defensive effort.
Indeed, the majority of the game's best chances fell to the home side, with Felipe Anderson and Andriy Yarmolenko both looking lively on the flanks. Chelsea were grateful for Michail Antonio's profligacy; one suspects that Marko Arnautovic, missing here through injury, would not have been so forgiving.
Alvaro Morata, on as a second-half substitute for Olivier Giroud, missed Chelsea's best opportunity when Lukasz Fabianski parried away his dink from close range, while Yarmolenko headed a gilt-edged chance wide at the other end.
This was the end of Chelsea's perfect start, but it was far from the first evidence this season that Sarri's men have a long way to go to trouble perfection.
2. Hazard won't score 40 goals playing like this
Sarri has been clearer than any of his Chelsea predecessors about what Hazard must do to score more often -- "spend less energy far from the goal and play in the last 25 metres" -- and there were signs in the first half at the London Stadium that the Belgian was attempting to action his head coach's instructions.
Twice he attempted to break West Ham's offside trap by darting onto long, floated passes over their defence; the first occasion was halted by a raised flag, the second resulted in a tackle from the recovering Fabian Balbuena. But such direct running without the ball remains the exception rather than the rule for Hazard.
Old habits are hard to shake, and throughout Hazard's career at Chelsea he has been required to be a key creator as well as scorer. When you have the talent to do anything it is often hard to know what you should prioritise, and even harder to put into practice when it goes against your long-established instincts.
It didn't help that after a bright start, much of Jorginho and Mateo Kovacic's more ambitious ideas came to nothing. But the reality is that despite several incisive dribbles, the man tasked by Sarri with troubling the 40-goal mark this season left the London Stadium without registering an effort on target.
Twice in the second half Hazard's nature overrode his new role in this team, as he tried to play in Morata with an overly ambitious back-heel and a first-time aerial flick rather than attempting to trouble Fabianski himself.
Chelsea need their superstar to start thinking more like a wide forward and less like the winger he has always been if they are to avoid more days like this, particularly if Pedro's absence proves a lengthy one and goals continue to elude Morata and Giroud.
3. Signs of weakness ahead of Liverpool
Chelsea's results in the early weeks of this season have thrust them into the Premier League title conversation, but their performances on the pitch have rarely approached anything like the quality produced by Manchester City and Liverpool. This was a truer reflection of where they are as a team.
Sarri still has question marks in all areas. Up front, neither Giroud nor Morata is a dependable goal scorer. The midfield is overloaded with passers, while Kante is being asked to do a Frank Lampard impersonation minus any of the finishing skill. Many of Chelsea's attacks are crippled by a general lack of width.
But it is in defence that Sarri will have the most concern as he prepares to face Liverpool's formidable front line next weekend.
The inherent danger in Chelsea's expansive passing game was laid bare whenever they lost the ball against West Ham, with routine interceptions often ending in Felipe Anderson and Yarmolenko running directly at the centre-backs.
Marcos Alonso, while an excellent footballer, is most certainly not a full-back and the thought of Mohamed Salah running at him in transition -- with David Luiz the last line of defence behind the Spaniard -- should fill Sarri with dread.
Jurgen Klopp has designed his Liverpool side and system to sow chaos in possession teams. City could not live with them three times out of four meetings last season, and Chelsea at this stage are simply City-lite in style and quality.
It's not difficult to imagine Sarri's high defensive line being torn to shreds, particularly if Rudiger's injury deprives the Blues of all recovery speed. Liverpool will certainly be the test of Chelsea's fledgling title aspirations, but there is little evidence to suggest it is one they will pass.