Momentary lapse means Dundalk will need to produce huge performance at Rosenborg after Oriel draw
Dundalk still have a shot at the next phase of the Champions League - but their route to bigger things and greater riches could have been a lot smoother had Stephen Kenny's side not shot themselves in the foot tonight.
David McMillan moved into third place in the list of all-time League of Ireland scorers in European competition when he headed Dundalk into the lead at home to Rosenborg.
But it was a sloppy and poorly-defended away goal, just before half time, which could prove to be the pivotal goal in this tie as, with this 1-1 draw, Dundalk now need to score in the away leg in Trondheim next week to advance to the third qualifying round.
Dundalk may quibble with the decision to award the free which led to Rosenborg's goal, a minute before half time, but they failed to defend a fairly basic set piece and defender Tore Reginuissen was able to get a shot in, which appeared to then get a deflection from Dundalk skipper Brian Gartland and creep over the line.
On the basis of their blistering start to this game at a sold-out Oriel Park, all 3,111 seats in the house occupied, Dundalk did deserve something, but they were unable to sustain that pace and tempo once Rosenborg had levelled, they didn't trouble the away keeper Anders Hansen in the second half despite the input of subs Dylan Connolly and Ciaran Kilduff, and had to settle for a 1-1 draw.
Kenny suffered the biggest defeat of his 41 European ties as boss in Bohemians' 4-0 loss away to Rosenborg in 2003 but he now needs to summon up potentially the biggest win of his career back in Trondheim next week, though their good away record in Europe means it's anything but Mission Impossible.
This was always going to be a tough one for Dundalk, as their pairing with Rosenborg in last month's draw was just about the hardest draw they could have faced.
The Norwegian side have that knack of negotiating those occasionally tricky early rounds in Europe and the side from Trondheim have got past the first hurdle, at least, in every one of their last 15 European campaigns. Rosenborg losing out in the early rounds of Europe is as unlikely as the Dublin senior footballers not making it to the Leinster final.
In fact, the question was posed whether even the Dundalk side of 2016 at their peak could have dealt with the men from Norway, bearing in mind that every player in the Rosenborg starting XI was a senior international.
But there was not even a hint of an inferiority complex from the home side, as they tore into Rosenborg from the off, putting the away side under sustained pressure.
Michael Duffy had been a threat from the early stages while Patrick McEleney prodded and passed in midfield.
Despite that home pressure, Rosenborg were still shocked to go behind on 18 minutes. The side have scored some cracking goals in Europe under Kenny but this goal, on 18 minutes, was more basic than beautiful, but no less important.
Duffy''s ball in front the left was not dealt with by a Rosenborg defence comprised of four senior Norwegian internationals, and McMillan was free to head home his seventh goal in the Champions League, a record for a League of Ireland player.
Losing in Ireland was not part of the deal for Rosenborg and they responded well, with Dundalk keeper Gary Rogers called to to make two essential saves.
A minute after Dundalk's lead goal, Rogers leaped high to deny Nicklas Bendtner a certain goal, and on the half-hour mark Rogers again saved Dundalk, keeping out an effort by Pal Andre Helland.
Rosenborg remained patient and, just before the break, they got their equaliser. A softly-awarded free kick created a softly-conceded goal, Eggen Hendenstad's free kick not cleared by Dundalk and Gartland sadly, it seems, got the last touch, poking the ball past his own keeper.
With so much experience in their side, Rosenborg knew that at 1-1 away from home their job was largely done and they bedded in for long periods in the second half while Dundalk's only real threat was a headed effort in injury time from sub Kilduff.
They have won big European games away from home before but Dundalk now need one of their biggest-ever efforts if they are to avoid an early Euro exit.