The visitors had been on course to claim a draw in Portugal, but Sporting scored twice in time added on to take all three points.
First, Paulinho headed home from a corner in the 91st minute and then, moments later, Arthur Gomes cut in from the flank, left Emerson Royal all ends up and finished past Lloris.
The defeat was Spurs’ first since April and ended Antonio Conte’s side’s unbeaten start to this season. Skipper Lloris believes it was a reminder about the level required when playing in Europe’s elite competition.
“In the last few moments of the game, I believe that if you cannot win the game, you do everything to not lose it,” he said. “From this corner we have to focus to not concede this goal. There were some moments in the game we managed well, other moments they had good chances.
“There is a lot of regret, because we could have got something.
“It’s a reminder. Every team, every player, they play at their best in this competition, as we saw from the Sporting players. They had a great team performance.
“We feel there is a gap for improvement, but we know [that], so the only judgment you can have is about points, about wins. There were some good actions from us, but it’s all negative because we lose. This is the feeling after the game. Only the score matters.”
Defeat capped off a frustrating night for Spurs. Heung-min Son again failed to get off the mark, while Harry Kane also had a rare off-night.
In contrast, Sporting’s front line looked sharp, thanks largely to the performance of former Spurs academy graduate Marcus Edwards.
“It feels great, winning at the end like that. We deserved it,” he said. “It was a strange feeling playing against Spurs, but it was good to see people I know.”