Sporting scored in the 90th minute and again in stoppage time to beat Tottenham 2-0 on Tuesday and make it two wins from two to open the Champions League group stage.
Both goals came from substitutes – Paulinho and Arthur Gomes – as Tottenham slipped to its first loss of the season in all competitions.
Paulinho glanced in a header from a corner to the near post to give the lead to the Portuguese team, which spent most of the game under pressure and looking to hit Tottenham on the counterattack.
Gomes sealed the win when he finished off a solo run down the left wing by cutting in and poking a shot past Tottenham goalkeeper Hugo Lloris.
Tottenham started Group D with a 2-0 win over Marseille last week but only after scoring late goals with the French team down to 10 men.
Sporting opened by beating Eintracht Frankfurt 3-0 away.