Leigh Griffiths and Celtic had mixed feelings after qualifying for the Europa League knockout stages despite defeat at home to Salzburg.
The Hoops made a dismal start, falling behind to two volleys from Alan inside the first 13 minutes.
Stefan Johansen pulled one back but Griffiths saw his close-range header saved in Celtic's best opportunity for an equaliser, and Naby Keita made it 3-1 in injury time.
However, Dinamo Zagreb's 1-0 loss at Astra in the other Group D game meant Ronny Deila's side are uncatchable by both those sides with only a trip to Croatia remaining.
Griffiths said: "We're disappointed to lose the game.
"I had great chance to make it two each, the goalie's made a great save but I've got to do better.
"But the boys put in a great performance, we're through now and we're delighted."
Griffiths has had to wait for his chance in the line-up and said: "I was just delighted to get a start, I was cramping up near the end but hopefully I've done enough to put myself in contention for Sunday (against Hearts in the Scottish Cup). I've said I had to work hard and wait for my chance and I've taken it tonight."
The Scottish champions were in disarray in the early stages as Brazilian striker Alan struck twice in a dramatic first 13 minutes and the visitors might have stretched their lead before Hoops' midfielder Johansen reduced the leeway with a drive on the half-hour mark.
The home side dominated the second period but could not get back on level terms before Salzburg sub Keita grabbed a breakaway third in injury time.
Despite the importance of the fixture, the match had failed to capture the imagination of the Hoops fans.
The top tier of the 60,000-capacity stadium remained unopened for the visit of Salzburg whose boss Adi Hutter wanted his team to become the first Austrian side to win on Scottish soil.
As expected skipper Scott Brown returned from suspension to take his place in the Celtic midfield while Efe Ambrose replaced the injured Jason Denayer.
Griffiths was handed his first start since August in the absence of ineligible striker John Guidetti and midfielder Callum McGregor also came in from the cold as James Forrest and Kris Commons dropped to the bench.
Salzburg had their Spanish captain Jonatan Soriano spearheading the attack along with Alan who stunned the home fans twice in a spectacular opening.
The first goal came when midfielder Massimo Bruno cut in from the left and when his right-footed drive from 25 yards deflected off Charlie Mulgrew, it fell fortuitously to Alan and he quickly fired past the helpless Craig Gordon.
Alan was soon to add his second as Celtic toiled.
It was painful viewing for the Celtic fans but the home side revived their fortunes in the 30th minute when Johansen swept an Emilio Izaguirre cross past Peter Gulacsi from just inside the box.
As the game wore on Celtic peppered Salzburg's box with crosses but in the three minutes of added time they were undone again when Keita headed in a third on the counter-attack.