Last season's runners-up Tottenham Hotspur squandered a two-goal lead to draw 2-2 in their Champions League Group B opener away to Greek club Olympiakos Piraeus on Wednesday.
Tottenham silenced the raucous crowd with two goals in four minutes midway through the opening half, first with Harry Kane's well-struck penalty and then a stunner by Lucas Moura.
Olympiakos, who had conceded only once in nine games in all competitions so far this season, halved the deficit through Daniel Podence shortly before halftime.
The hosts levelled it up after 54 minutes when Mathieu Valbuena beat fellow Frenchman Hugo Lloris from the penalty spot after some sloppy play by the visitors.
Tottenham looked the more likely winner in the closing stages with Dele Alli and Erik Lamela squandering chances.
While it was an improvement on their start in last season's ultimately memorable Champions League campaign, when they lost their opening two matches, Tottenham will be disappointed at their failure to protect their lead.
They will need to be far more clinical when they host Bayern Munich in their second game. Olympiakos will travel to Red Star Belgrade next.
"When you go 2-0 up after 30 minutes you are in a great position, after that I thought we controlled the game whereas before we didn't play well but scored two goals," Kane said.
"The goal just before halftime changed the momentum and it's disappointing from our point of view. We have to improve.
"We wanted to get off to a winning start and put ourselves in a great position."
Tottenham welcomed back big-money signing Tanguy Ndombele after injury, handed Alli his first start of the season and gave Lucas Moura, hero of last season's semi-final win over Ajax Amsterdam, the nod ahead of Son Heung-min.
But they were slow to get going and were given an early wake-up call when Miguel Angel Guerrero's first-time volley rebounded back off the post after a chested lay-off by Podence.
Tottenham took the lead against the run of play in the 26th minute when Kane was needlessly tripped by defender Yassine Meriah and handed out punishment with an unstoppable penalty.
Moura then showed an exquisite first touch from Ben Davies's pass to thump a shot past keeper Jose Sa.
It was harsh on Olympiakos but they responded well with Valbuena's pass slicing open Tottenham's defence and Podence's low shot going in off the post.
Tottenham invited trouble early in the second half when Christian Eriksen was caught in possession on the edge of his area and Valbuena was fouled by Jan Vertonghen.
Referee Gianluca Rocchi pointed to the spot and after a lengthy delay for a VAR check, Valbuena converted the penalty.
Alli had a shot well-saved by Sa and Lamela tried his luck from a tight angle as Tottenham raised the tempo but Olympiakos stretched their unbeaten run at home in Europe to 10 games.
City put aside domestic slip with 3-0 win at Shakhtar
ManchesterCity put aside their recent Premier League setback, delivering a comfortable performance in a 3-0 win at Shakhtar Donetsk in Champions League Group C on Wednesday.
Pep Guardiola's side, beaten by NorwichCity on Saturday, brought in their Brazilian former Shakhtar midfielder Fernandinho as a makeshift central defender to replace the injured John Stones.
But there was to be no real test of City's back line as the English champions dominated, taking the lead in the 24th minute through Riyad Mahrez, who slotted home after Ilkay Gundogan's shot came out off the post.
Shakhtar quickly had a chance to go level after a superb run from Taison who found Junior Moraes but his tame shot was well dealt with by Ederson.
City doubled their lead in the 38th minute with Mahrez finding Gundogan at the end of a trademark City passing move and the German clipped home to make it 2-0.
The Ukrainian side struggled to break up City's possession play in midfield and while there was a relaxed tempo from Guardiola's side, the outcome was never in doubt.
Gabriel Jesus made it three in the 76th minute after Kevin De Bruyne led a swift counter-attack and slipped in the Brazilian who made no mistake.
There was some good news on the injury front for City with French left-back Benjamin Mendy coming on as an 83rd-minute substitute, for his first appearance since April.
Dynamic Dinamo hand Atalanta sour Champions League debut
Dinamo Zagreb made a perfect start to their Champions League Group C campaign when a majestic performance gave the Croatian side a 4-0 home win over Italian rivals Atalanta on Wednesday.
Midfielder Marin Leovac fired Dinamo ahead in the 10th minute before a Mislav Orsic hat-trick sent Atalanta reeling on their debut in Europe's premier club competition.
Dinamo coach Nenad Bjelica, whose adventurous yet unfamiliar 4-3-3 formation turned out to be a masterstroke as it kept Atalanta on the back foot throughout, was delighted.
"I had a gut feeling it would bear fruit and it did thanks to a perfect first half," Bjelica told a news conference.
"We were tight at the back and pressed their midfield hard, which in turn enabled us to create a lot of chances. They didn't expect that because we'd never played in this formation before."
The score did not flatter the home side, though, as they missed several chances to win by a bigger margin, having ripped into the visitors with crisp one-touch passing and darting raids down both flanks.
Atalanta barely threatened and missed their best chance after the damage had already been done, as Dinamo keeper Dominik Livakovic pulled off a magnificent save to deny Duvan Zapata.
Leovac opened the floodgates when he slid in to meet a perfect Petar Stojanovic pass from the right and blasted it into the roof of the net from close range, with Atalanta keeper Pierluigi Gollini a mere bystander.
Leovac turned provider in the 31st minute after he left his marker for dead on the left flank and squared the ball back to Orsic, who side-footed it sweetly into the bottom left corner of the net from the edge of the penalty area.
Another raid by Stojanovic produced the third goal in the 42nd minute, as Arijan Ademi met the right back's deep cross at the far post and headed it back for Orsic to nod in the ball from two metres.
Livewire Orsic completed a memorable night with a superb finish from 16 metres in the 68th minute, applying a perfect first touch to control a lofted pass into his stride before driving an unstoppable shot past Gollini.
Orsic credited his brilliant individual performance to selfless teamwork.
"I am happy about the hat-trick of course but the team did a great job tonight," he said.
"It was our best performance in the last two years and we are now in a good position to reach the knockout rounds."
In the group's other fixture, ManchesterCity romped to a 3-0 win at Shakhtar Donetsk.
City are at home to Dinamo in the next round while Shakhtar visit Atalanta.
Brugge and Galatasaray ends goalless
Club Brugge and Galatasaray played out a goalless stalemate in their opening Champions League Group A game at the Jan Breydelstadion on Wednesday.
Both teams hit the woodwork in an otherwise uneventful match ahead of the much-awaited clash between Paris St Germain and Real Madrid in the same group.
Brugge had the best chance in the first half when Federico Ricca's strike hit the crossbar and the Turkish side also went close on the hour with Sofiane Feghouli's effort brushing the top of the bar.
The Belgians were also denied a late penalty after a VAR review for a possible Marcao handball three minutes from time.
Galatasaray next host PSG and Brugge travel to Real Madrid on October 1.