Belgian league leaders Antwerp secured a shock 1-0 win over Tottenham Hotspur and AC Milan extended their unbeaten run to 23 games as they won 3-0 against Sparta Prague in the Europa League on Thursday, while Arsenal cruised to a 3-0 win over Dundalk.
Veteran striker Lior Refaelov's first-half goal gave Antwerp their second win in Group J and put them top with six points, three ahead of Spurs and LASK of Austria.
Antwerp dominated the first half and went ahead just before the half-hour mark after a defensive lapse by Ben Davies allowed Dieumerci Mbokani to steal away the ball and set up the Israel international for a solid finish.
Four substitutions at the start of the second half reflected the irritation of Spurs manager Jose Mourinho, but Antwerp continued to look the more dangerous despite the changes.
Harry Kane came on for Gareth Bale 13 minutes into the second half, but the Spurs skipper was also unable to ignite a comeback as Antwerp proved defensively solid to hang on for the win.
In the other game in Group J, Austrian side LASK got the better of Ludogorets, beating the Bulgarians 4-3.
A penalty miss by Zlatan Ibrahimovic had little impact on AC Milan as they cruised to victory against Sparta Prague to go top of Group H with two wins from two games, while Scottish champions Celtic threw away a two-goal lead in a 2-2 draw at Lille.
Alderweireld's hometown dream remains unfulfilled in Antwerp
Three quick goals either side of halftime gave Arsenal a comfortable victory over Dundalk that puts them top of Group B on goal difference ahead of Molde, who grabbed a 1-0 home win over Rapid Vienna.
There was drama in Group C as 10-man Bayer Leverkusen slumped to a shock 1-0 defeat away to Slavia Prague, and Nice edged out Hapoel Beer Sheva by the same scoreline to leave all three sides on three points after the first two rounds.
The goal of the night was scored by Omonia Nicosia's Jordi Gomez, who struck a quick free kick from just inside his own half that flew over PSV Eindhoven keeper Yvon Mvogo and into the net.
Unfortunately for Gomez, his superb effort was in vain as Donyell Malen scored twice in reply, netting the winner in the 90th minute for a 2-1 victory to go second in Group E behind Granada, who drew 0-0 with PAOK Thessaloniki.
The spoils were shared in Group A as AS Roma were held to a surprise 0-0 draw by Bulgarian side CSKA Sofia, while CFR Cluj of Romania went top after a 1-1 draw with Swiss side Young Boys.
In Group L Hoffenheim made it two wins out of two with a 4-1 win over bottom side Gent, while El Fardou Ben Nabouhane scored twice as Red Star Belgrade went second with a 5-1 drubbing of Slovan Liberec.
In Group F, Napoli defeated La Liga leaders Real Sociedad by 1-0.
Group G is turning into a two-horse race as Leicester City beat AEK Athens 2-1 away and SC Braga won by the same scoreline at Georgian side Zorya to leave both victors with six points from two games.
Benfica are top of Group D after defeating Standard Liege 3-0 while Steven Gerrard's Rangers made it two straight wins as they edged past Lech Poznan 1-0.