Tottenham’s sole chance of silverware now hanging in the balance after Lucas Bergvall's own goal in the 18th minute earned AZ a deserved lead ahead of the second leg in North London. Spurs failed to muster a shot on target until the 88th minute and Son admitted that his side were pathetic and need to improve drastically.
"It's nowhere near where we should perform," Son told TNT Sports. "It was very disappointing that we performed like this, including me. It's a big wake-up call because next week is the biggest game of the season.
"We didn't create anything in the first half, sloppiness, not performing the way we should. Everyone is very disappointed about the individual performance and the team performance.
"There are no excuses, we were not good enough. It's just 1-0, it's still not finished, and next week we have to be much better."
Tottenham manager Postecoglou pointed out in September that he always wins a trophy in his second season at a team but the he says that will not happen if his side do not up their game.
"It was nowhere near the level it needed to be," Postecoglou said of his side's performance in Alkmaar.
"It wasn't great from us tonight, pretty much all facets of the game. We didn't really get to grips with any part of the game. We struggled to gain any momentum with the ball, we weren't as aggressive as we needed to be without the ball.
"I don't think it's a matter of effort or attitude. I don't think it is going out there and not trying, but, like I said, we didn't really come to grips and have the right mindset to tackle an away fixture in Europe.
"You are going to face some pressure when you play away from home in Europe and weather the storm and get to grips with it, but we never really did so that was a disappointment."
Son spoke later after the game to SpursPlay and says they are lucky to have a second leg where they can salvage the game and push on to the next round.
"We are going to have to move on. We have already passed this game and it was basically very, very poor. Luckily, we have another chance to play at home and we can turn around again in a positive way. It is too early to let heads down and give up. We have a massive, massive chance next week and we need to be ready to try to turn it around.
"We should be lucky we have another chance next Thursday ... Every opponent you play you have to respect massively because it’s a hard competition and everyone wants to win. Everyone can talk (about) who is favourite but, at the end of the day, who wins is the most important thing.”