Chris Coleman's charges dominated the opening stages, with Gareth Bale particularly instrumental, only for Grant Hanley to head the home side into a surprise lead on the stroke of half-time.
|9/1||Scotland are 9/1 with BetVictor to draw 0-0 with Serbia
"It was a freak 25 minutes," the Scottish boss told reporters. "I can't call it a bad 25 minutes. I thought it was freaky, what I [saw] was totally unusual."
"I spoke to the players and they had never seen anything like that 25 minutes anywhere in their footballing career. I don't think that will ever happen again - I know it won't happen again."
Strachan went on to admit that morale was low after the loss, with the defeat "an opportunity wasted".
"We are still in the process of making ourselves feel better and we will do that by training and putting together a plan," he continued.
"We are all hurting, that's for sure. The players realised that it was an opportunity wasted and I realised that as well."