He felt his team did not get anywhere close to peak performance in the 2-1 loss against Aberdeen.
Neilson watched from the stand serving the last of a three-game touchline suspension as John Souttar’s first-half penalty was overhauled by goals from Marley Watkins and Lewis Ferguson.
That brought an end to Hearts’ 11-game unbeaten league run and confirmed just two points taken from nine available last week.
“We have played three games in a week but that's no excuse,” Neilson told the Evening News. “They are all fit boys and they’ve been magnificent from day one. Saturday was just one of those days when we just didn’t click.
“We were getting pressed, then when we did get through we didn’t get the link and support. It was a frustrating day all round. We just weren’t anywhere near the level we have been at.
“Right from the start, I thought we weren’t there. We didn’t pass the way we usually pass it, we weren’t rotating the way we normally do, we weren’t taking the ball on the half turn.
“We tried to change things to get us into the game a bit but in the second half we lost two poor goals. The first one comes in, Craig Halkett mistimes it and the boy [Watkins] gets a shot. For the second goal, they get a block at a set-play [on Beni Baningime].
“I won’t say too much on it but I didn’t think we played at the level we should do. We know what is expected here and that’s why we didn’t get three points from the game. We need to be better than that all over the pitch.”
Andy Halliday’s late red card for a challenge on Ferguson left Hearts with ten men. “You’re playing up at Pittodrie, there is always a wee bit of aggro and energy,” said Neilson.
“He’s made a tackle and the referee deemed it a red card. Was it? If he had given a yellow card and settled things down, probably everyone would have accepted it.”