Celtic showed second-half fight but were ultimately outclassed away to Benfica as they were beaten 4-1 in the Europa League.
Defensive mistakes from Celtic helped Marco Silva's hosts race into a three-goal lead by the break, with Jhon Duran at the double and Alexander Bah on the scoresheet.
Camilo Duran - who had made his own way to Portugal after staying in Scotland for the birth of his child - pulled one back for Martin O'Neill's side and hit a post as Celtic tried to set up a grandstand finish.
But instead, Vangelis Pavlidis wrapped up the scoring and a comprehensive win for Benfica, which leaves Celtic with two defeats from their first two games in the league phase. Celtic have also lost four of their last five in all competitions.
There may have been encouragement in some of their second-half attacking play but alarm bells were ringing at the back. Nonetheless, Celtic boss O'Neill stayed positive afterwards, telling TNT Sports: "Overall, I'm really, really delighted with the second-half performance and it's a shame we conceded the three goals first of all."
In Lisbon, the city which hosted Celtic's greatest moment in the 1967 European Cup final, the visitors handed Benfica a head start when Dane Murray kicked the back of Jhon Duran's leg in a crowded box. The former Aston Villa striker was cool with his panenka penalty.
Sebastian Tounekti then switched off for Bah to volley in before Auston Trusty and Celtic keeper Vijami Sinisalo contrived to let Jhon Duran score from what appeared an impossible position for the third.
Celtic were desperately unlucky not to bring the game back to 2-1 before that, with Kasper Hogh hitting a post from close range before Camilo Duran curled the rebound against both the crossbar and the other post. And it would not be the last time the frame of the goal was rattled.
Fredrik Aursnes nodded against a post at the other end, from what was eventually flagged an offside position, while Andreas Schjelderup and Tomas Araujo hit the woodwork in the second half, with Camilo Duran's strike against an upright in between. Fine margins in those moments - but the difference between these sides was far greater.
4: PENALTY TO BENFICA! Murray kicks Jhon Duran in the back of the leg as he goes to make a clearance in a crowded penalty area.
5: GOAL! DURAN WITH THE PANENKA! Cool as you like from the Colombian striker who dinks in the opener.
23: GOAL! It's cute from the impressive Gianluca Prestianni, who lifts a cross into the box for Bah to volley in - but it's terrible from Tounekti, who goes to sleep and allows Bah to run off him and into space to convert.
25: SIDE-NETTING! Jhon Duran fires the wrong side of the near post and Celtic are on the ropes here.
28: CELTIC SO UNLUCKY! Hogh volleys against the upright from Tounekti's cross before Camilo Duran bends a follow-up shot against the crossbar and post.
35: OFF THE POST! But the offside flag goes up. Jhon Duran meets a corner and heads it into the six-yard box but Fredrik Aursnes nodded against the post before being flagged offside.
36: GOAL! Trusty tries to show Jhon Duran away from goal but the striker hooks his foot around the ball and somehow angles an effort past Sinisalo at his near post.
63: GOAL! Camilo Duran pulls one back for the Hoops, heading in sub Haissem Hassan's cross.
72: OFF THE POST! Sub Alex Oxlade-Chamberlain feeds Camilo Duran in the box and he crashes a left-foot strike against the near upright!
74: OFF THE POST! Andreas Schjelderup now goes close for Benfica!
89: GOAL! Pavlidis runs in behind and clinically fires low into the net from the edge of the box to make it 4-1.
90: OFF THE FRAME AGAIN! Araujo heads Pavlidis' cross against the bar!
Celtic boss Martin O'Neill to TNT Sports:
"It's the last thing you want to do, concede so early on. At 2-0 we have a great chance to make it 2-1 and then in a few minutes they make it 3-0. We could have capitulated but I thought the second half performance was really terrific.
"We created chance after chance, we should have scored more goals, and of course you're going to leave yourself a bit open at the end. But this second-half performance gives me the determination. I think we can still qualify. I know it's down to six games. We can still do it.
"We came roaring back [in the second half], the substitutes did brilliantly and we could have scored a number of goals. Yes, I accept the fact that then, on the break, they could have scored themselves - as they did for the fourth goal.
"But overall, I'm really, really delighted with the second-half performance, and it's a shame that we conceded the three goals first of all."
Celtic captain Callum McGregor to TNT Sports:
"A disappointing result. We're here to try to get points and win but we played against a really good side, with really good quality in the final third. First half we didn't really help ourselves, in terms of the unforced errors that lead to the goal, but second half gives us a bit to hang onto in terms of performance. We scored one, could have scored another couple as well. A game of two halves."
