David Moyes' reign as West Ham manager began in disappointing fashion as the Hammers were beaten 2-0 at Watford to remain in the Premier League's bottom three.
The Scot was chosen as Slaven Bilic's successor during the international break, but defeat in his 500th game as a Premier League boss was as painful as the 26 he suffered with relegated Sunderland last term as missed chances at one end were punished by the goals of Will Hughes and Richarlison at the other.
Watford had lost their three previous matches and doubts remain over the future of boss Marco Silva, who has been linked with the vacant position at Everton, but West Ham showed little progress from the 4-1 loss to Liverpool that saw Bilic meet his end at London Stadium, with Hughes' first Premier League goal securing an 11th-minute lead.
An equaliser could and should have followed, only for the Hammers to find Heurelho Gomes in inspired form before the goalkeeper's Brazilian compatriot Richarlison sealed the points in the second half.
Another blow was to come for Moyes as club-record signing Marko Arnautovic was forced off in the final 20 minutes with an apparent hand injury.
The win takes Watford into eighth - just five points shy of the top four - while West Ham are 18th ahead of Friday's clash with Leicester City as Moyes prepares to make his home bow.
Moyes' first big decision was to recall Andy Carroll to the starting line-up for the first time since his red card at Burnley last month and the striker took just six seconds to land an eerily similar elbow on Watford debutant Marvin Zeegelaar, although he escaped punishment.
If that early clash worryingly resembled what had gone before under Bilic, West Ham's inauspicious start only continued with the sloppy opener. Andre Gray prevented the visitors from clearing a left-wing cross and his miskick fell kindly for Hughes, who swept a finish into the bottom-left corner.
As the Hammers floundered in their attempts to muster a response, Carroll's frustration grew further and he was booked for an off-the-ball barge on Richarlison.
Joe Hart parried away a low curler from the industrious Richarlison - Kiko Femenia driving the rebound wide - before West Ham belatedly worked Gomes at the other end as the goalkeeper bravely blocked Cheikhou Kouyate's effort.
And Gomes made another stunning stop to close out the first half, somehow reaching Arnautovic's deflected header and then springing up to save the rebound too.
Kouyate blazed a huge chance over the top from Arnautovic's centre after the restart and Abdoulaye Doucoure almost punished the visitors' profligacy as he whipped a 20-yard strike just beyond the left-hand post.
It was Hart's turn to make a point-blank save when he brilliantly turned away Adrian Mariappa's downward header, but the England international perhaps should have done more to deny Richarlison the second goal. The Brazilian's shot, following Hughes' pass, slipped through the goalkeeper's grasp and into the net.
The troublesome Carroll was withdrawn and Arnautovic soon followed as he fell in a challenge with Zeegelar and writhed in pain as he awaited attention.
Although West Ham kept pushing, a stunning goal-line clearance from Christian Kabasele kept Manuel Lanzini at bay and Watford saw out the closing stages with relative ease.
