Steve Evans cited the lack of a goalscorer for his side's poor recent run of results following their 1-0 defeat at Leyton Orient.
O's striker Kevin Lisbie struck in the 27th minute when he stabbed the ball into the net from close range after Millers goalkeeper Adam Collin had blocked a shot by Dean Cox and then pushed the midfielder's follow-up effort onto the crossbar.
It was Lisbie's 12th goal of the season, while Rotherham worked hard in the second half and enjoyed the greater possession without troubling O's keeper Jamie Jones.
"Everyone knows that we lack a goalscorer and that was shown, two or three good chances came our way, but we never made their goalkeeper work," Evans said.
"I think to be fair, it was a game of two halves and our defending was poor for their goal.
"They were allowed to dominate the first half, it seemed that we had turned-up for a tea party in London, but in the second half they couldn't get out of their half.
"But we didn't make their goalkeeper work and you are not going to score a goal if you don't make the keeper work.
"In the second half we've dominated the leaders from the start to the end, yes they've counter-attacked and Adam (Collin) has made some good saves but by that time, we had five up-front. We had them hanging-on at the end.
"I'm disappointed for the players because they've given absolutely everything and they've nothing left.
"We didn't get too many decisions, we never showed in the first half but after, we played as we could play and I wouldn't think Orient had been outplayed like they were here for a long time.
"When you are up at the top of the league, you tend to get the rub of the green and decisions go your way."