The New Saints face a tough task to reach the third qualifying round after they lost 3-1 to Polish champions Legia Warsaw at Wrexham.
Wednesday night marked a year on from when TNS drew with Swedish champions Helsingborgs - but there was no repeat this time around.
It is the Welsh Premier League champions' 15th European campaign but it could well come to an end next week in Poland following their loss.
Legia were inches away from taking the lead when Marek Saganowski hit the woodwork with less than 10 minutes gone.
However, TNS took a surprise lead two minutes when Ryan Fraughan scored and they almost doubled their lead four minutes before the break when Alex Darlington hit the woodwork.
However, the second half was only two minutes old when Legia levelled through Michal Kucharczyk.
The Polish side then went ahead 10 minutes later through former Southampton striker Saganowski and they went on to dominate.
Jakub Kosecki had a shot blocked and the Poles forced a series of corners before Michael Wilde missed an opportunity to equalise with a little more than a quarter of an hour remaining.
They were made to pay for that when Kosecki scored Legia's third goal a minute later and Kucharczyk squandered a good chance in injury time.
Daniel Chima's first-half goal means Sligo face an uphill battle to keep their Champions League dream alive at Molde's expense.
The Nigerian struck three minutes before half-time at The Showgrounds as Ole Gunnar Solskjaer's men earned an advantage to take back to Norway for Tuesday's return leg.
Ian Baraclough's men were disappointing in the first half and their only noteworthy effort on goal was a 24th-minute shot from Evan McMillan, which was saved.
Jo Inge Berget hit the woodwork seven minutes before half-time but the hosts did not heed the warning and fell behind four minutes later when Chima broke through.
The 2012 Irish League champions pressed hard for an equaliser in the final quarter, with Joseph Ndo, Jeff Henderson, Lee Lynch, Kieran Djilali and Alan Keane all threatening.
However, Molde maintained their advantage and are now firm favourites to reach the third qualifying round.