For the full house in attendance – Roy Keane among them –as well as those looking in from the 37 countries who were showing the game live, it would have been hard for much of this night to tell the giants and giant-killers apart, as Zenit were forced to come from a goal down to take the three points back to St Petersburg.

But, despite this defeat, the Irish champions remain second in the Group D table and with every reason to still believe they can qualify for the knock-out stage.

Hard-working physios and a couple of days of rest and recovery helped minimise the injury damage to Dundalk going into the game, with skipper Stephen O’Donnell the only full absentee – albeit a significant one given his influence throughout the season - while John Mountney, who’d been struggling with a back problem, was at least able to make the bench.

Talent-heavy Zenit could afford to make light of a couple of no-shows of their own, with star names and experienced internationals Axel Witsel, Robert Mak and skipper Javi Garcia all present and correct in an attacking line-up spearheaded by Russia’s Artem Dzyuba and Brazil’s Giuliano.

The consensus before kick-off was that, despite Dundalk having confounded expectations since the beginning of their great European adventure – not least on this very ground when they beat BATE Borisov 3-0 - this game against a team of vast financial wealth and serious Champions League pedigree would prove a step up too far.

But after only six minutes, it was the home side, showing admirable composure from the off, who came agonisingly close to taking a giant step in the game, Ronan Finn racing on to a David McMillan pass which opened up the Zenit defence and, from the right hand side of the area, driving his low shot just an inch or two wide of the far post.

Despite manager Stephen Kenny’s mischievous talk of eschewing the ‘low block’, a defensively disciplined Dundalk were, as it turned out, quite prepared to string six white shirts across the back to keep the multi-pronged Zenit attack at bay. But, with their trademark pace and intensity, the Irish champions were also committed to getting bodies forward whenever the opportunity allowed.

Zenit, as might be expected, were dominating the possession stats yet failing entirely in the opening phase to directly threaten Gabriel Sava in the Dundalk goal. Indeed, on numerous occasions, the visitors’ lengthy spells of keep-ball ended up with them going back to Yuri Lodygin in their own goal.

Ten minutes before the break, Dundalk came close again when, after the Zenit defence failed to properly clear their lines following excellent work by Patrick McEleney in getting a cross in from the end line, Dane Massey sent a looping header back towards goal which, though it looked like Lodygin got a touch to help the ball over the bar, failed to get even the reward of a corner.

Next, a linesman’s flag was correctly raised when Brian Gartland, free in the box, headed a Daryl Horgan free straight at the Zenit ‘keeper.

And so the first 45 came to a close, Zenit having seen plenty of the ball, but Dundalk the side who, from much less possession, had created the better chances to break the deadlock.

If there was a fear for the Lilywhites going into the second half, it was that the prodigious levels of mental and physical effort which had already gone into containing Zenit, and the additional surges of energy involved in trying to hurt them on the break would, coming on the back of such an intensive schedule and protracted season, take its toll.

But in the 53rd minute Dundalk discovered that Lady Luck wears white, as Yuri Lodygin made a complete hash of dealing with a speculative and not particularly firmly hit effort from outside the box by Robbie Benson, the keeper practically diving away from the bouncing ball which, to the astonished joy of the players and supporters, ended up nestling in the back of the Zenit net.

In danger of losing the plot as well as the game, the frustrated Russians were now accumulating yellow cards at a rate of knots before, just past the hour mark, they had the post to thank for preventing them from going two behind, Dane Massey’s header coming back off the upright from a beautifully flighted Daryl Horgan free.

But on 70 minutes it was the turn of Dundalk ‘keeper Sava to have a moment to forget as he skied a Chris Shields back pass only as far as the edge of the area and, when Guliano headed the ball through to the unmarked Robert Mak, the man who had tormented Scotland in their recent 3-0 defeat to Slovakia, kept his cool to slot home.

On 76 minutes it was two to the visitors, and this time Dundalk could have no complaints, with Belgian international Axel Witsel twice involved in a fluent, incisive move which was finished emphatically from close range by the impressive Giuliano.

In the final minute of normal time, Brian Garland conceded a penalty with a tired-looking, mistimed tackle on Mauricio but the substitute was unable to put a gloss on the scoreline which Zenit would scarcely have deserved, Sava comfortably saving his spot kick.

DUNDALK: Sava, Gannon, Gartland, Boyle, Massey, Benson (Mountney 78),Finn, Shields (Shiels 85), Horgan, McEleney, McMillan (Kilduff 71).

FC ZENIT: Lodygin, Anyukov, Neto, Lombaerts, Criscito, Shatov (Kokorin 61), Javi Garcia (Mauricio 71, Witsel, Mak (Djordjevic 78), Dzyuba, Giulano.

Referee: Miroslav Zelinka (Czech Republic)