Ian Sharps scored the only goal of the League Two game three minutes before half-time at St James Park on Saturday when he glanced Ben Pringle's corner into the net, but the Millers were reduced to 10 men late in the game when substitute Mitchell Rose was sent off just two minutes after coming on.
The Grecians had plenty of possession, especially in the second half, but they did not test Rotherham goalkeeper Andy Warrington enough.
"I am very disappointed that we lost, but I am not too unhappy with the way we competed," Tisdale said. "Again, it becomes very difficult when you concede the first goal and that has happened too often this season. I find it very hard to criticise the players for their commitment and their effort and they certainly had enough about them to have got something from the game.
"We knew we would get a tough game from them and they picked their game up after a couple of poor results. We could have got the first goal, we didn't have too many chances although Jamie (Cureton) had a shot saved and Alan Gow hit the crossbar, but they were fair game for their 1-0 lead at half-time.
"It was a very difficult day with the conditions as they were, but I thought the pitch was fantastic and I enjoyed it. I'm just disappointed with the result. We have had a very good week or two, I am not going to be too unhappy with the way the players have played and there is plenty to take from these last two weeks."