Lucas Bergvall struck late for the 1-0 win in London, though escaped a second yellow card just moments earlier. The Swede cut down Reds fullback Kostas Tsimikas in the lead-up to the winner.
Slot later said: "I don’t think there’s any debate about it. I think I saw Ange (Postecoglou) sitting here on Saturday and Spurs weren’t happy with a few decisions.
"One went against them, tonight maybe one went in favour of them.
"The decisions is made, you can’t change it. When he didn’t give the second yellow card, no one thought it would have such a big impact 30 seconds later.
"I am 99.9 per cent certain I was not the only one who didn’t feel the best when it went in. It was, for him (referee Stuart Attwell) also far from ideal."
Reds captain Virgil van Dijk also said: "I think it was quite obvious it was going to be a second yellow (for Lucas Bergvall).
"I think it was pretty clear. It was a coincidence and a minute later he scores the winner.
"It is what it is. He (the referee) made a mistake in my opinion and I told him that. He thinks he didn't but it was quite obvious I think and everyone on the sidelines knew it was supposed to be a yellow.
"There's a linesman there, a fourth official there, there's VAR, a referee and he doesn't get a second yellow. I'm not saying this is the reason why we lost tonight but it was a big moment in the game."