Tottenham Hotspur suffered their first defeat of the season as Sporting snatched a 2-0 home win over Antonio Conte's side in the Champions League on Tuesday with goals in added time from substitutes Paulinho and Arthur Gomes.
Spurs created the better chances in an open and entertaining match but Sporting striker Paulinho broke the deadlock in the 90th minute with a glancing header from a corner.
Brazilian forward Gomes, who had only come onto the pitch after the goal, made sure of the victory with a superb strike in the second minute of added time, finishing from close range after a breathtaking run into the box.
The victory means Sporting lead Group D with six points, with Tottenham second on three after two games.
There was a minute's silence to commemorate the death of Queen Elizabeth II, which led to all matches in the United Kingdom scheduled for last weekend being postponed and leaving Spurs with extra time to prepare for the trip to Portugal.
Tottenham's Richarlison, who scored both goals in last week's 2-0 win over Olympique de Marseille, had the ball in the net late in the first half but his effort was ruled offside.
Moments later, former Spurs trainee Marcus Edwards almost scored a remarkable individual goal, dancing his way from the halfway line into the area before playing a one-two with Francisco Trincao and then shooting at goal, only to be denied by the leg of goalkeeper Hugo Lloris.
Richarlison missed further chances in the second half while Harry Kane narrowly failed to get on the end of a low cross from Ivan Perisic after the Croatian had torn down the left wing.
The game looked to be heading for a draw until Sporting midfielder Pedro Porro went on a late marauding run and curled a shot towards goal which Lloris just managed to tip over the bar.
His effort galvanised the home crowd and the team responded to grab a victory that gives them control of the group.