Celtic's bid to reach the Champions League last-16 will go to the wire after a 2-1 defeat at Benfica gave the Portuguese side hope of pipping them to the post.
After upsetting Barcelona on the previous group stage matchday in perhaps the second-best result in the club's history, the Glasgow side travelled to the city of their undoubted peak - the 1967 European Cup final win over Internazionale - with a chance of securing a top-two finish with a game to spare.
But despite Georgios Samaras equalising after Ola John's early goal - giving the visitors the minimum result they needed for 39 minutes - they could only withstand the hosts' onslaught for so long and Ezequiel Garay's volley on 71 settled the contest.
Both teams now sit on seven points apiece, and while Celtic will fancy their chances at home to Spartak Moscow with Benfica travelling to the Camp Nou, the Hoops will now be without the suspended Victor Wanyama following his second-half booking.
Barcelona’s 3-0 win at Spartak Moscow earlier in the day had simplified Celtic’s mission somewhat: the Russians were no longer a threat, and a score draw at Estadio da Luz would be enough for the knockout phase.
But the home side put an early dent in Neil Lennon’s aspirations when Eduardo Salvio’s low cross from the right was deflected into the path of John after Oscar Cardozo and Scott Brown cancelled each other out.
The Liberian forward was composed and slotted home the seventh-minute opener to send the half-empty home stands into raptures. A task few supporters had faith in suddenly looked possible early on.
Initially, Jorge Jesus’s men were well set up to hold onto their lead, as their disciplined shape allowed the Bhoys only an occasional glimmer of hope on the counter.
But the same could not be said of their set-piece marking, as minutes after Cardozo was sent racing through and should have doubled the lead, Samaras rose at the far post to convert the equaliser.
The score as it stood was enough to send Celtic through, but as they had for the opening seven minutes while level, Benfica went back on the assault.
Disaster almost struck for the away side five minutes before the break when Kelvin Wilson’s sliding challenge in the slippery conditions took out team-mate Brown, but vigilant last-ditch defending prevented the Super Eagles from punishing the numbers disadvantage.
And a number of successive blocks closed down constant Benfica pressure on the stroke of half-time to get the Scottish champions half-way through the mission at hand.
Things would not get any easier after the interval as the Lisbon outfit continued to pour pressure onto Fraser Forster’s goal.
Celtic had defender Adam Matthews to thank on 53 minutes as the young Welsh defender produced a tremendous double block, first stopping Rodrigo Lima’s shot on the line before closing down the dangerous Cardozo as he collected possession 10 yards from goal.
Luisao headed over on the hour mark and Lima somehow did not get a finishing touch to John’s fine low centre from the left 10 minutes later, but the match-winner would soon follow.
A Benfica attempt to head a delivery back across goal had been thwarted by Efe Ambrose at the expense of a corner, from which the head-tennis routine yielded a better result as Luisao guided the ball into the path of fellow centre-back Garay, whose finish was that of a prolific striker.
The tiring Scottish side had finally been broken down after working tirelessly to keep on level terms, and Salvio almost doubled the lead moments later with a speculative 25-yarder which cannoned off the crossbar.
Substitutes Kris Commons and Tony Watt had chances to snatch a qualification-clinching leveller in the dying embers, but did not trouble Artur in the Benfica goal.
Watt’s cross-shot deep into stoppage time at the end could have been converted by Gary Hooper, who could not react quickly enough to stick out a leg as the ball flashed across goal.
Celtic must now trump Benfica’s result on the final match day to beat them to second spot in Group G behind winners Barca.
MAN OF THE MATCH
Luisao - Benfica: Strong at the back and even claimed the crucial assist for defensive partner Garay's winner.
BENFICA - Artur 7, Luisao 9, Garay 8, Andre Almeida 6, Matic 7, Perez 6, Cardozo 7, Lima 7, John 8, Salvio 8, Melgarejo 6. Subs: Maxi Pereira 6, Jardel n/a, Gaitan 7.
CELTIC: Forster 8, Lustig 7, Ambrose 6, Wilson 6, Matthews 8, Brown 6, Wanyama 7, Ledley 6, Mulgrew 5, Hooper 5, Samaras 7. Subs: Kayal 7, Watt 5, Commons 6.