Rotherham boss Steve Evans knows his side were taught a harsh lesson after Watford staged a late show in a 2-0 win at New York Stadium.
Evans watched his side, playing their third game on their return to the second tier, put in an impressive display for much of the game, but they failed to make their chances count as Paul Taylor squandered two good opportunities while Lee Frecklington had an effort deflected just wide.
And Watford, who were well below what is expected of them this season, made the Millers pay with two goals in the final 17 minutes through Lloyd Dyer's first league strike for the club Gianni Munari's late tap-in.
That left Evans ruing his side's inability to score when on top.
"It's tough to take, until they score a goal they have been outclassed and outplayed," the Scot said.
"We were terrific against a top class side who I think will win promotion.
"We have given them a hiding but they have gone with the points. For 75 minutes we were far the better side, but they have taken a couple of chances. If we had gone in front it would have been a different matter.
"I think they will go away and know it has been a tough night. I'll go and have a glass of wine and lick my wounds. We played some fantastic football, with seven or eight players playing who were in League Two.
"It was a hard lesson but that is what Championship football is about. But if we play like that we will have no issues.
"It was a special performance and we are very unlucky to be going home without adding to our points tally."
For Watford it was a perfect response to Saturday's 3-0 drubbing at Norwich and boss Guiseppe Sannino was pleased his team selection was justified.
The Italian made five changes to his side and stands by his decision.
"We have 24 players and if I have 24 players then they can all play different matches," he said. "For me, it was important to give these players a start so I did.
"We played Norwich and we did a lot of running and I needed fresh legs and the result justified it.
"The result was fair to me against a very good team with aggressive players who play good football. Winning here is difficult and we can go home with three points."
Dyer caused a stir with his goal celebration as he appeared to run over to the Watford dug-out and shout at his manager, perhaps angry at not starting in South Yorkshire.
However, Sannino played down the incident, saying: "I didn't see it. But his celebration was normal."