Maurice Edu scored a dramatic last-gasp goal to send Rangers into the last 16 of the Europa League as Sporting Lisbon crashed out of the competition.
El-Hadji Diouf claimed his first goal for Rangers before goals from former Rangers midfielder Pedro Mendes and Yannick Djalo appeared to have secured victory for the home side at the Jose Alvalade Stadium.
But Edu pounced in injury-time with the decisive goal in the tie as Rangers triumphed on away goals after the first leg had ended 1-1.
Afterwards, Walter Smith claimed he was thrilled with the win, even though the dramatic triumph means even more fixture congestion.
The Scottish champions remain in the hunt for four trophies this season following the away goals win in Lisbon. That means they still have to juggle domestic commitments with Europe with a small squad depleted by injury.
But Smith said: "We will have to wait and see how the season unfolds before we see if there is any great impact.
"You can't pick and choose. We would never consider it an inconvenience qualifying for a round in Europe. We are pleased to do so. There's a pressure on Scottish clubs to do as well as they can so that our co-efficient level gets as high as possible. "
Rangers also defeated Sporting en route to the Uefa Cup final in 2008. Smith, when quizzed on whether he believes his side can go all the way this time around, added: "The circumstances which surround the club at the moment are totally different from when we were in the Uefa Cup a few years ago. We can only try and get through the games as they come along."
Next up for Rangers is a trip to face PSV Eindhoven on 10 March after the Dutch defeated Lille. Smith added: "It's a good result for PSV because Lille have been doing well in the French league. But PSV have also been doing well so it will be an extremely difficult match."
With a 1-1 draw in the first leg at Ibrox, the tie was tipped in the favour of Sporting ahead of tonight's clash at the Jose Alvalade stadium. But their away goal advantage was wiped out when Diouf netted the opener and his first goal for Rangers.
The home side looked set to progress when they hit back through goals from Mendes and Djalo. But the Scots left it late when Edu grabbed the tie's decisive goal in injury-time. Smith said: "We are pleased to get through.
"We started the game slowly but we managed to get a goal. There wasn't much between the teams in the second half at all. With the circumstances of getting the goal, we are pleased to progress.
"We are disappointed with the way we lost the first goal as we should have handled it better. Overall it is a system that has been reasonably successful in European games this season."
Sporting Patricio, Pereira, Polga, Torsiglieri, Evaldo, Mendes (Carlos Saleiro 81), Abel, Fernandez (Coelho 90), Zapater, Djalo, Postiga (Andre Santos 86). Substitutes not used Tiago, Maniche, Solomao, Cristiano.
Rangers McGregor, Foster, Bougherra, Weir (Lafferty 71), Papac, Whittaker, Davis, Bartley, Fleck (Weiss 71), Edu, Diouf (Healy 82). Substitutes not used Alexander, Wylde, Hutton, Cole.
Referee P Tagliavento (Italy)