30 November 2019 - Chelsea were poor, sloppy and wasteful as they fell 1-0 to Manuel Pellegrini's West Ham United. It meant back-to-back defeats for Frank Lampard and pretty much sparked the inconsistency which has plagued the Blues' season.
For West Ham, it marked the end of a seven-game winless run and proved that the Hammers do actually have the talent to hang with the best, even if they like to keep that talent hidden deep down a little too often.
The two sides will meet again on Wednesday at the London Stadium, in a game which could well end up defining both teams' respective season.
The defeat back in November at Stamford Bridge hurt Chelsea. Frank Lampard's young side had harboured tentative hopes of challenging for the Premier League title and had won seven of their last nine games. The two defeats came against Liverpool and Manchester City.
It's not as if they weren't dominant during the game. Chelsea had 19 shots on goal and could have easily converted a lot of them. Christian Pulisic, Mason Mount and Pedro were all guilty of spurning great chances - a theme which has become all too common this year.
Nobody has claimed that Chelsea don't play good football under Lampard. They can create a boat load of opportunities in front of goal, but as this defeat proved, they don't always have the players to finish things off.
That was evident during losses to Everton and Bournemouth which came soon after and has also been on show during some of the Blues' victories this year - 2-1 victories over both Tottenham Hotspur and Aston Villa were both tough to watch.
Lampard's men have powered on past that loss to West Ham and find themselves in a good position in the race for Champions League qualification. Their counter-attacking 2-1 win over Manchester City proved Chelsea can succeed with smash-and-grabs, but how about when they're the favourites?
The onus is on Chelsea to play the football against West Ham, just as it was in November. The Blues weren't good enough back then, but a victory on Wednesday would go a long way to proving just how far Lampard's side have come in the space of just a few months. It's time for Chelsea to step up and prove they can dispatch of the so-called smaller sides.
Anything other than three points would leave Chelsea panicking in pursuit of fourth place and could even suggest that the Blues aren't good enough to qualify for Europe anyway. It's a must-win game against a team who now only care about points, not performances.
Chelsea may want three points, but West Ham need the points.
Pellegrini led West Ham to tenth last season, and although no fan will openly admit it, there were quiet hopes that the Hammers would sneak into Europe this year, especially after the signings of Sébastien Haller and Pablo Fornals.
The 5-0 loss to City on opening weekend was an anomaly as West Ham embarked on a six-game unbeaten run. They were fifth in late September, but then things fell apart.
Seven games without a win took a toll on West Ham, but they managed to bounce back with a spirited performance against Chelsea. Aaron Cresswell's goal got the job done and Michail Antonio had a second ruled out. West Ham were by no means great, but they showed they can get points.
So, if they are clearly able to get points, why haven't they?
Pellegrini was sacked one month after this game and replaced with David Moyes, who hasn't been able to reverse the curve. West Ham now sit 17th, level on points with Bournemouth in 18th.
If there was ever a time to get those points, it's now.
Last time out against Tottenham, West Ham looked determined but out of ideas, and they fell to a 2-0 defeat. That's how this season has gone for the Hammers - all the gear but no idea - and now their Premier League safety is on the line.
A performance like the one they pulled out against Chelsea in November would go a long way to saving West Ham, but anything close to the level they've generally been at this year won't be good enough. It's now or never.
We already know a lot about both these teams, but we could know even more by Wednesday evening.
Are Chelsea ready to control the race for the top four? Do West Ham have what it takes to survive? Let's find out.