Tottenham Hotspur slumped to a shock 1-0 Europa League defeat at Royal Antwerp on Thursday, while Serie A leaders AC Milan eased to victory over Sparta Prague.
Jose Mourinho's Spurs failed to create a single chance of note in a lifeless display, with Gareth Bale, who re-joined the club on loan from Real Madrid in the close-season, lasting less than an hour before being substituted.
The surprise win takes Antwerp to the top of the early Group J table after their opening 2-1 victory at Ludogorets last week.
The Belgian outfit are playing in the main stage of a European competition for the first time since a UEFA Cup first-round loss to Newcastle United in 1994.
The hosts took the lead just before the half-hour mark, with Dieumerci Mbokani robbing makeshift Spurs centre-back Ben Davies before feeding Israeli forward Lior Refaelov to drill a fierce shot into the corner.
Antwerp wasted a golden chance to double the lead in the 54th minute, as Congolese striker Mbokani contrived to fire the ball over an open net when only three yards from goal.
Mourinho threw on Harry Kane and Son Heung-min for Bale and Dele Alli in search of an equaliser, but again it was their opponents who should have scored when Norwegian wing-back Simen Jukleroed ran clean through on goal and blazed wildly over the bar.
Spurs dominated possession but never seriously threatened, and the Antwerp players were able to celebrate a famous triumph in an empty stadium.
Milan made it two wins from two in Group H with a 3-0 success over Sparta, despite Zlatan Ibrahimovic missing a first-half penalty.
Goals from Brahim Diaz, Rafael Leao and on-loan Manchester United wing-back Diogo Dalot saw Milan extend their unbeaten run to 24 matches in all competitions.
Stefano Pioli's side sit two points clear of Lille at the top of the group, after the French outfit fought back from two goals down to grab a 2-2 home draw with Celtic.
Jamie Vardy netted a spot-kick as Leicester City made it back-to-back victories in Group G with a 2-1 win at AEK Athens, while Paco Alcacer scored a late double as Villarreal saw off Qarabag 3-1 in Group I.