The visitors have returned from lockdown in winning form, whereas the Hammers have lost two from two so far to plunge their Premier League survival hopes into even greater doubt.
Frank Lampard will certainly not relish the chance to nudge his boyhood club that bit closer to relegation on Wednesday, but he showed just how demanding he is of his Chelsea players at the weekend.
The club-record goalscorer pulled no punches in his assessment of his side's performance against Leicester City, despite Chelsea making it through to the semi-finals of the FA Cup for a 10th time since the turn of the century.
Lampard made three half-time subs and admitted that he wanted to make more, and so he will be demanding another response from his players despite them heading across London on a five-match winning run across all competitions.
Part of the manager's thinking may have been to ensure that there was no drop-off in performance levels after last Thursday's 2-1 victory over Manchester City - a result which saw Pep Guardiola's side surrender the title to Liverpool.
While the celebrations in West London after that result were nothing compared to those on Merseyside, the importance of the win over City for Chelsea should not be overshadowed by the fact that it had even bigger implications elsewhere.
Had Chelsea lost that match then they would be heading into this contest fifth in the table, but as it is they still enjoy a two-point lead over Wolverhampton Wanderers with a game in hand over Nuno Espirito Santo's side.
Wolves and Manchester United are doing a good job of keeping the pressure on Chelsea, though, and Lampard will know that there is little margin for error any more in a top-four race which has been defined by inconsistency so far.
The Blues could, however, create another barrier of protection from the chasing pack should other results go their way this week, with Leicester City now just one point ahead of them in third place and Chelsea in far better form than the team they knocked out of the cup.
Chelsea will certainly be bigger favourites to beat West Ham than Leicester are to beat Everton, although the Hammers are approaching must-not-lose territory themselves.
David Moyes's side are still lingering on the right side of the dotted line when it comes to relegation, but only by virtue of having a goal difference two better than Bournemouth's and five better than Aston Villa's.
Fortunately for West Ham their relegation rivals are also in poor form, but with things so tight at the bottom of the table the Londoners know that they will need to turn their own form around sooner rather than later.
West Ham have won just once in the Premier League in 11 games since New Year's Day, and this calendar year no team has lost more than their eight top-flight games - including five of their last six.
Moyes's side have not even scored since returning after lockdown, falling to back-to-back 2-0 defeats against Wolverhampton Wanderers and Tottenham Hotspur, while another blank immediately before the break means that they are now in danger of going four Premier League games without finding the back of the net for the first time since October 2006.
Despite those grim statistics, West Ham's record at the London Stadium since Moyes took over is much improved - two wins and two defeats from five games so far this calendar year, having only picked up one point from their previous six home games.
However, over the course of the entire season only Southampton have amassed fewer points on home territory, and West Ham are unlikely to be able to rely on their away form either with seven successive league defeats on the road.
West Ham Premier League form: LLWLLL
Chelsea Premier League form: LWDWWW
Chelsea form (all competitions): DWWWWW
Chelsea could be without one of their star men since the restart, with Christian Pulisic being taken off against Leicester after feeling tightness in his calf.
The extent of the injury has not yet been determined, but with such a quick turnaround between fixtures Lampard is unlikely to take any risks over a muscle problem.
Andreas Christensen missed out entirely at the weekend due to a hip problem which is not thought to be serious but will be assessed ahead of this match, while Fikayo Tomori is closing in on a return from his muscle problem.
Sunday's match-winner Ross Barkley will be hoping to have earned a starting role, while the likes of Cesar Azpilicueta, Kepa Arrizabalaga, Olivier Giroud and Marcos Alonso are pushing for inclusion in the XI too.
Arthur Masuaku will be assessed due to an ankle injury, but Moyes has no new injury concerns after last week's defeat to Tottenham.
West Ham possible starting lineup:
Fabianski; Fredericks, Ogbonna, Diop, Cresswell; Soucek, Rice; Fornals, Noble, Anderson; Antonio
Chelsea possible starting lineup:
Kepa; Azpilicueta, Rudiger, Zouma, Alonso; Barkley, Kante, Kovacic; Willian, Giroud, Loftus-Cheek
We say: West Ham 1-2 Chelsea
Chelsea may have only won one of the last five meetings between these two sides, but the formbook points at there only being one result in this one.
Chelsea are enjoying one of their best runs of the season, whereas for West Ham it is difficult to see where the next win is coming from. They need one as soon as possible if they are to get themselves away from trouble, but it would be a surprise to see it come in this match.