If they are to realise their ambition of reaching the last 16 from a group in which they are quoted at 66-1 to win, a false start could be fatal.
Given how much Celtic rely on their home form – they have won 13 of their 18 group stage games at Parkhead, losing only once, to Barcelona in 2004 – it would be a real hammer blow if they did not put three points on the board at the first time of asking.
This is, at once, a moment to savour and a moment of truth, and Lennon purred: "To bring these nights back to Celtic Park is fantastic.
"We're all looking forward to getting started now. I think we're ready.
"We have worked very, very hard to get to where we are. Now the players want to make their names in this competition."
Apart from Scott Brown, those available for selection tonight are entirely inexperienced at this level.
A win would provide this group of players the belief they not only belong, but can be competitive when up against Europe's elite.
With a difficult trip to Moscow to follow, the last thing Lennon needs is for his side to 'do a Scotland' and put themselves behind the eight-ball from the start of their qualifying campaign.
The minimum target has to be eight points. The best chance of this is from home wins against Benfica and Spartak Moscow, and draws squeezed out of the ties in Russia and Portugal.
With the Barcelona double header in the middle of the group fixtures, and anything earned there very much a bonus, it is the start and end of the campaign which will determine Celtic's continued involvement in the Champions League after Christmas.
The monkey has been taken off their back in terms of away games with the victories in Helsinki and Helsingborgs.
However, this is a stiffer test altogether, and one which will examine every facet of the side Lennon has built over the last two years.
Any shortcomings will be cruelly exposed. This is an arena where you are assuredly only as strong as your weakest link and, on recent evidence, for Celtic that would appear to be their defence.
Sure, they lost only one goal in the four qualifying ties, and have had three clean sheets since Helsinki took a shock lead at Parkhead back at the start of August.
But neither of the Scandinavian sides had a Cardozo, Lima or Rodrigo firing their bullets.
Benfica boss, Jesus Jorge, has only one way of playing – attack – and, with defensive problems of his own, he will send his side out to keep the play as much in the Celtic half of the pitch as possible.
Lennon is ready for this, and has been working hard to hone the counter-attacking skills of his side.
That will require patience to be shown and nerve to be held, not only by his players, but from the supporters who have bought into the excitement of their club's return to the Champions League stage.
The manager has planned for this night, not just since the draw was made, but from the time he was informed he would be given the chance to take over from Tony Mowbray.
He said: "In the Champions League, you have to be a bit more tactically prepared and a bit more patient.
"This is not a British-type game. Possession is key, and you have to be very good on the ball and concentrate for the 90 minutes."
However, despite meticulous homework and preparation, Lennon is helpless when the moment comes for his players to carry out his bidding – as was shown at Perth on Saturday.
Their lacklustre effort against St Johnstone shocked as much as disappointed him, and he accepts he will not know until the game begins tonight how his men will embrace the occasion and the demands which come with it.
How that old warhorse would love to be out there in the middle of the action.
One of Lennon's greatest qualities in the very successful Celtic team managed by Martin O'Neill was to ensure that, not only did he step up to the plate against the best Europe had to offer, but that everyone around him gave maximum effort as well.
Is there a character in this side who can provide such a fulcrum for what is required?
Brown wears the armband, but his on-going injury issues are effecting his ability to influence games.
So, it will be down to every player selected to show they have the courage to meet the challenge which Champions League football presents.
"I want to see them express themselves and play the football we know they are capable of," said Lennon, like a proud father sending his kids out into the world.
"We know they're in for a very tough game against an excellent side. But we don't just want to be also-rans in this group. We are going to compete."
Benfica – who reached the quarter-finals last season – will be a good measure of how far they have already travelled.
But The Eagles have played only three competitive games, and could be vulnerable given that they have been out of action for two weeks due to the international break.
This has not helped them to bed in the new arrivals who replaced Javi Garcia and Axel Witsel, key men sold for big bucks as the transfer window was preparing to close.
By the time Celtic travel to Lisbon to meet them again in November, the Portuguese champions will be a much more dangerous animal.
So, first blood has to be drawn by Lennon's Bhoys.