Holders Real Madrid were two minutes from losing at home to Sporting Lisbon in their opening group game before staging a late comeback to win 2-1.
Bruno Cesar’s second-half goal looked to have given the Portuguese side a memorable triumph at The Bernabeu, yet ex-Sporting forward Cristiano Ronaldo popped up with a late leveller before Alvaro Morata snatched a winner four minutes into stoppage time.
Borussia Dortmund had no troubles elsewhere in Group C as they recorded a 6-0 demolition of Legia Warsaw in Poland.
Mario Gotze, Sokratis Papastathopoulos and Marc Bartra all scored in the opening 18 minutes and Raphael Guerreiro, Gonzalo Castro and Pierre-Emerick Aubameyang added more goals after half-time.
Juventus were held to a 0-0 draw by three-time Europa League winners Sevilla in Italy, while Porto and Copenhagen also shared the spoils having drawn 1-1, with ex-Cardiff striker Andreas Cornelius scoring for the visitors.
Bayer Leverkusen, who led 2-0 after 15 minutes, could only draw 2-2 at home with CSKA Moscow in Tottenham’s group but Lyon had no such issues at home, recording a comfortable 3-0 success over Dinamo Zagreb.