Despite blowing a two-goal lead in the first leg before rescuing a 3-3 draw, Ian Foster’s side did not let an advantage slip against the Luxembourg outfit for a second week running.
In fact, the tie was as good as over as a contest inside the opening 16 minutes, when the Lilywhites – playing their first European tie at Oriel Park since the visit of Kispest Honved in 1991 – raced into a two-goal lead.
After going close twice in the opening minutes through Neale Fenn and a Fahrudin Kuduzovic strike that came back off the crossbar, Dundalk were gifted an opportunity to open their account when Iclandic referee Magnus Thorisson awarded them a penalty in the fifth minute.
Wayne Hatswell’s cross from the left was neatly headed down by Tiarnan Mulvenna into the path of Kuduzovic but as the striker turned goalwards he was upended by Khalid Benichou, whose late own goal earned Dundalk a share of the spoils the previous week.
Neale Fenn then stepped up to take the spot kick and sent Oriel Park wild by sending Grevenmacher netminder Marc Pleiming the wrong way with a low drive into the bottom left hand corner.
Fenn then returned the favour for Kuduzovic 11 minutes later by turning provider for the home side’s second. The former Bohemians ace showed tremendous skill at the edge of the area to slip his strike partner through and Kuduzovic made no mistake with a composed finish.
Dundalk had a let-off four minutes after the restart when Adrien Baur raced onto a long ball out of defence before lifting it over the advancing Gregg.
However, the danger was averted by the alert Garry Breen, who headed over the crossbar to the relief of his goalkeeper.
That was about as good as it got for Marc Thome’s side, however, as Dundalk pushed hard for a third goal.
They were unlucky not to find it too in the 58th minute when Ross Gaynor got in behind the Grevenmacher defence only to see his effort turned away by the legs of Pleiming.
There was some consolation for the visitors in stoppage time when Christian Muller cut in from the right before rifling a low shot past Gregg into the bottom right hand corner.
DUNDALK: Gregg; Kelly, G Breen, Miller, Hatswell; Mulvenna (McGowan, 71 mins), Maher (McDonnell, 77 mins), Cawley, Gaynor; Fenn, Kuduzovic (J Breen, 90 mins).
CS GREVENMACHER: Pleiming; Pereira Gaspar (Brzyski, 72 mins), Heinz, Benichou (Lorig, 45 mins), Hoffman; Baur, Furst, Hartung, Mendes (Almeida Da Silva, 61 mins); Muller, Louadj.
Referee: Magnus Thorisson (Iceland).