A brace from on-loan Carlisle striker Paddy Madden either side of a James Hayter strike ensured the Somerset side got off to a dream start in 2013 by comfortably seeing off in-form Orient, who came into the game on the back of nine wins in their last ten matches.
"I don't think we set our stall out well enough in the early stages and they started as the better side and adapted to the conditions better than us," said Slade.
"It's the worst surface I've seen in League One for years, it's poor, but fair play to Yeovil because they adapted to it.
"Of course we missed Kevin [Lisbie] but there was no point in bringing him because he's had an injection in his shoulder which we need to settle, hopefully for the weekend.
"I haven't seen the first goal but the players think it's offside. In the end, whether it was or wasn't, we have stopped.
"They were very direct but it was effective.
"For the third goal it was again down to the conditions. Ben [Chorley] will probably wish he had put it in row Z, but unfortunately he under-hit the back-pass and it's been costly for us."