Raheem Sterling netted at both ends as Manchester City were made to fight for a 3-3 draw with Celtic in a Champions League thriller on Wednesday, while Atletico Madrid once again did for Bayern Munich.
While City's perfect start to the season was ended in Glasgow, their Premier League rivals Arsenal eased to a 2-0 victory against Basel.
Atletico had eliminated Bayern in the semi-finals last season and repeated the trick at the Vicente Calderon to make it a double for Spanish clubs against German opposition as Barcelona downed Borussia Moenchengladbach.
On paper, the Group C clash at Celtic Park appeared to be a bit of a mismatch with City looking to equal Tottenham Hotspur's English record of 11 successive victories at the start of a campaign from 1960.
But instead Pep Guardiola's men found themselves having to come from behind three times to claim a point at a raucous Parkhead, with Celtic first scoring in the third minute when an Erik Sviatchenko header went in off Moussa Dembele.
Fernandinho equalised only for a Kieran Tierney cross to go in off Sterling and restore the Scottish champions' lead.
Sterling's brilliantly-taken goal at the other end restored parity before the half-hour mark, but Dembele capitalised on an Aleksandar Kolarov error to make it 3-2 just after the break.
However, Nolito got City's third equaliser and it was the English side who looked more likely to go on and win it.
"I don't know how many the chances they had after the third goal. We should have won it," said Guardiola.
Meanwhile, Theo Walcott made the difference as Arsenal eased to three points against Basel at the Emirates Stadium.
The Swiss champions have enjoyed excellent results in European competition against English sides in recent years but a first-half brace by Walcott ensured it was a comfortable night for the Gunners.
In Madrid, Atletico inflicted Carlo Ancelotti's first defeat as coach of Bayern as Yannick Carrasco's first-half strike separated the sides at the Vicente Calderon in Group D.
The Spaniards eliminated Bayern on away goals in the semi-finals of last season's Champions League and there was to be no revenge for the five-time European champions, who would have lost by a wider margin had Antoine Griezmann not struck the bar with a late penalty.