Joe Royle felt some of his side switched off with the score at 4-1, but the Town manager praised Rotherham's spirit as they pulled the scoreline back to 4-3.
Royle said: "At 4-1 I felt we had the chance to improve our goal difference but all credit to Rotherham for their fightback. If they had played like that all season they would not be going down.
"We were giving the ball away in areas we shouldn't have done. Several key players switched off, deciding that the game was won.
"I am delighted that we are now clear in second place with a bit of daylight, but one or two of our players looked a little weary in their second game in four days.
"The first goal we conceded was like a Sunday morning goal but the Rotherham forwards gave us problems that other clubs hadn't been able to do. Perhaps it's easier to play when you know you are down and you can enjoy the pitch and the atmosphere."
Alan Knill, caretaker-manager at demoted Rotherham until the end of the season, is already looking to next season: "Relegation is a great disappointment but I think this squad includes players more than capable of bouncing back next year.
"We proved that tonight. The effort and ability should enable us to cope adequately in the division below.
"We were unlucky not to come away with something. No disrespect to Shaun Barker, but I'd rather one of our strikers had been in his scoring position at the end.
"On a bad night for the club there were plenty of positives from the performance. The best thing now is for the board to make a quick decision on the manager's position to provide more time to organise for next season.
"Ipswich are a top team and the match provided great entertainment, just what the neutrals want to see.
"When we were 4-1 down I wanted the referee to blow his whistle and end it all because I feared it could be six. But my players were brilliant the way they hit back and showed the conviction to push forward."