Watford taught Rotherham a harsh lesson about life in the Sky Bet Championship after they staged a late show at New York Stadium to win 2-0.
The Millers, playing just their third game back in the second tier following promotion last season, put in a rousing display for the much of the match yet were unable to convert a string of chances. And Watford, who were well below what is expected of them this season, handed down the sternest of punishments as two goals in the final 17 minutes won it.
Lloyd Dyer's first league goal for the club put them ahead in the 73rd minute and with the hosts pushing for a leveller Gianni Munari made sure of the points with five minutes to go.
Rotherham should have been out of sight by then as Paul Taylor wasted two chances and Lee Frecklington had an effort deflected, but they paid the ultimate price for their wastefulness.
That left Steve Evans' men with two defeats and just one goal from their opening three games and in no doubt where their early season problems lie.
For Watford it was the prefect response to a 3-0 drubbing at Norwich in midweek, though they will need to perform better if they are to be top-six candidates after Christmas.
The Millers came into the encounter full of confidence following the weekend's win over Wolves and perhaps sensing that the Hornets were not up for it, they set about their visitors early on.
Playing a high-energy pressing game they were the better team in the opening half-hour and limited Watford's highly-rated front pairing of Troy Deeney and Matej Vydra to scraps.
Although dominating, the hosts struggled to create chances until the 30-minute mark when Ben Pringle tested Heurelho Gomes with a curling effort from distance, with skipper Craig Morgan heading the corner over.
Evans' men continued to dictate the play and Taylor went close following a sublime piece of skill to control the ball before he cut inside and fired a shot just wide.
And they came within inches of ending a rousing first-half display in perfect fashion on stroke of the interval when Alex Revell's knockdown was hit first time by Frecklington but it took a nick off a defender and rolled just wide.
There was an equally good opening for the hosts, who did not let the break stop their flow, early in the second half as Taylor spooned over from 16 yards when he had time and space to pick his spot.
There was a definite sense that Rotherham's failure to score when on top was going to prove costly and Watford finally began to show a verve that has seen them labelled as potential promotion candidates this season.
And the Hornets did punish their hosts in the 73rd minute when Dyer reacted first to Adam Collin's parried save from Odion Jude Ighalo's shot and smashed home from eight yards.
The game was put to bed five minutes from the end when Munari had the easiest of tap-ins following good work down the left by Dyer and that is how it finished.