Slaven Bilic berated his West Ham players for an "unacceptable" performance after the high flyers crashed back to earth with a bump in a 2-0 defeat at Watford.
The Hammers, who kicked off in third following last week's win over Chelsea, had beaten Arsenal, Liverpool and Manchester City on the road this season.
But they came a cropper against the Hornets and, in particular, in-form striker Odion Ighalo as their unbeaten away record came to a sorry end.
Bilic said: "It was a collective bad day. I told the players it was unacceptable and to make sure it was a one-off.
"You are going to lose games in this league but we weren't good today, apart from in the first 10 minutes.
"We gave them the win. Watford were full of respect for us - but when they smelt that we weren't penetrating enough, and that our movement and passes were slow and backwards, they smelt the opportunity to go at us.
"We learned a lesson, and I see no reason why we won't come back and play like we did before."
The Hammers, without the injured Diafra Sakho, handed a first start since January to fit-again Andy Carroll.
But unfortunately for them, the big frontman was more involved in his own penalty area than the opposition's - with some calamitous results.
Carroll was West Ham's hero from the bench against Chelsea last week, but he got himself in an almighty mess from Ben Watson's free-kick, allowing Nathan Ake to drill in a cross which was turned in by Ighalo and defender Aaron Cresswell.
If there was any doubt about who got the final touch on that one, there was none just after the break when Ighalo collected Ikechi Anya's square ball and crashed an unstoppable drive into the top corner from 15 yards.
West Ham's misery was complete when, with four minutes to go, James Collins clattered into the back of Ighalo on the halfway line and was shown a straight red card.
Quique Sanchez Flores branded his side's display their most complete of the season so far.
"The boys did really well," said the Hornets boss.
"Everyone knows how important Ighalo is but a lot of players have the opportunity to score, "We are defending well and keeping he ball with confidence and a lot of players have ability to score.
"Was it our best performance? Yes, probably. I like it when we play football, and we defended well and played football with confidence. We are a tough team when we play like this."