Leyton Orient manager Russell Slade was left downbeat by the manner of his side's defeat at Rotherham.
Alex Revell's injury-time goal gave the Millers a 2-1 victory over their fellow League One promotion hopefuls.
Wes Thomas' goal put the hosts in front after 10 minutes, a lead they held until the 76th minute when Moses Odubajo fired Orient back on level terms.
But never-say-die Rotherham shocked the O's to steal the points when Revell netted the winner in the fourth minute of injury time with a perfectly placed shot - his third goal of the week after two on Tuesday night in the victory at Tranmere.
"It was very harsh to lose, we didn't deserve that ," said Slade. "We were excellent and got back in the game and we showed that normal character and grit.
"They started the better and possibly deserved the lead but by half an hour we were playing very well and the last 15 minutes of the first half we were back in the game.
"There weren't too many openings for both sides but we were working our way in and our goal came from a great opening and I thought that was exactly what we deserved.
"I don't think we managed the game well enough in those final few seconds and you have got to do that if you want to get promotions and get success. That was probably our poorest part of the entire game.
"It was an eagerness to try and get down the other end and get the win. We had worked so hard to get back in the game and we were in the dying seconds. And turning the ball over in the dying seconds has cost us dearly."