Kirk Millar bagged the only goal of the game as Linfield claimed a famous Champions League victory over Norwegian opponents Bodø/Glimt at Windsor Park.
The 30-year-old struck with an exquisite finish seven minutes from time to hand David Healy's side a huge advantage going into the return leg next Wednesday.
He dispossessed Marius Høibråten just outside the right side of the area before bringing the ball into the box and sending a deft chip beyond the reach of keeper Nikita Haikin into the opposite corner of the net.
Scoreless at the break, both sides had their chances in the first half with Glimt coming close through Joel Mugisha, Elias Hegan and captain Ulrik Saltnes while, for Linfield, Millar sent a stinging effort into the side netting.
The visitors had two efforts cleared off the line in the second half. Hugo Vetlesen saw a 55th minute volley headed away by Chris Shields before, around 20 minutes after that, substitute Amahl Pellegrino's low shot was blocked by Stephen Fallon.
Linfield take their slender lead with them to the Arctic Circle next Wednesday with the overall winners of the tie going forward to meet either Lithuania's FK Zalgiris Vilnius or Swedish giants Malmo. Zalgiris currently hold a one-goal advantage.
Linfield: Johns, Roscoe, Shields, Millar, Stewart, McDaid, Hall, M. Clarke, Finlayson, Fallon, Mulgrew subs Walsh (not used), Newberry (not used), McClean (replaced Mulgrew 64), McKee (not used), Devine (not used), Vertainen (replaced McDaid 64), Pepper (not used), Quinn (replaced Stewart 87), A. Clarke (not used), Palmer (not used), Archer (not used)
Bodø/Glimt: Haikin, Sampsted, Høibråten, Wembangomo, Amundsen, Vetlesen, Espejord, Saltnes, Hagen, Sørli, Mvuka subs Andersen (not used), Pellegrino (replaced Sørli 66), Boniface (replaced Espejord 66), Konradsen (replaced Hagen 86), Vetti (not used), Sjøvold (not used), Nordås (not used), Tjærandsen-Skau (not used), Koomson (replaced Mvuka 86)