There were big wins for Manchester City and Borussia Dortmund on Wednesday as matchday one concluded in the Champions League group stages.
Pep Guardiola's City signalled their intentions to challenge for the title after they hammered Borussia Monchengladbach 4-0 at the Etihad Stadium.
A hat-trick from Sergio Aguero (8', 28' pen, 77') secured the comfortable win for the Citizens and Kelechi Iheanacho added a fourth in stoppage time to wrap things up.
Borussia Dortmund were ruthless in their Group F opener as they put six unanswered goals past Legia Warsaw at the Pepsi Arena.
There were six different goal-scorers for BVB with Mario Gotze (7') breaking the deadlock before Sokratis Papastathopoulos (15'), Marc Bartra (17'), Raphael Guerreiro (51'), Gonzalo Castro (76') and Pierre-Emerick Aubameyang (87') all got in on the act.
Meanwhile, defending champions Real Madrid were handed a scare as they came from behind to beat Sporting CP 2-1 at the Santiago Bernabeu.
After a goalless first half, Bruno Cesar gave the visitors a 48th-minute lead, but Los Blancos hit back in dramatic fashion with two very late goals from Cristiano Ronaldo (89') and Alvaro Morata (90') securing the comeback win.
Tottenham got their European challenge off to a bad start after going down 2-1 to Monaco at Wembley, with all three goals coming in the first half.
The visitors went ahead on the quarter-hour mark through Bernardo Silva before Thomas Lemar doubled their advantage 16 minutes later, but Toby Alderweireld halved the deficit on the stroke of half-time to keep Spurs in the contest, although the Principality outfit held on for a precious victory.
Elsewhere, Juventus and Sevilla had to settle for a share of the spoils after their clash in Turin ended goalless, while 10-man FC Copenhagen came from behind to earn a 1-1 draw with FC Porto at Estadio do Dragao.
Otavio gave the Dragons a 14th-minute lead, but the Danish club hit back in the second half with an equaliser from Andreas Cornelius (52'), although they had to hang on for the final 24 minutes after Jan Gregus received his marching orders.
Leicester's debut in the competition went off without a hinge as they beat Club Brugge 3-0 at the Jan Breydel Stadium.
The Foxes raced into a sixth-minute lead through Marc Albrighton before a superb free-kick from Riyad Mahrez (29') doubled their advantage. The Algerian winger bagged a brace on the night after he scored from the penalty spot on 61 minutes to cap off a fine performance from Claudio Ranieri's side.
Goals from Corentin Tolisso (13'), Jordan Ferri (49') and Maxwel Cornet (57') ensured that Lyon made a winning start in the Champions League group stages after they beat Dinamo Zagreb 3-0 at Parc Olympique Lyonnais, while CSKA Moscow came from two goals down to draw 2-2 with Bayer Leverkusen at the BayArena.
Two goals in the space of six minutes from Admir Mehmedi (9') and Hakan Calhanoglu (15') put the hosts in the driving seat early on, but the Horses replied before the half-time break as Alan Dzagoev (36') and Roman Eremenko (38') scored in quick succession to clinch a share of the spoils.
Manchester City 4-0 Borussia Monchengladbach
Bayer Leverkusen 2-2 CSKA Moscow
Tottenham 1-2 Monaco
Legia Warsaw 0-6 Borussia Dortmund
Real Madrid 2-1 Sporting CP
Club Brugge 0-3 Leicester City
FC Porto 1-1 FC Copenhagen
Juventus 0-0 Sevilla
Lyon 3-0 Dinamo Zagreb