Gretna's European debut ended in crushing defeat as lethal Derry City all but assured their place in the first round proper of the Uefa Cup.
Kevin Deery (left) hit two of Derry's five goals at Fir Park
Ryan McGuffie gave Gretna an early lead but Darren Kelly responded for Derry as honours remained even at the interval.
But the second-half was dominated by some masterclass finishing from Derry as they beat Gretna into submission.
Both Kevin Deery and Ciaran Martyn bagged braces as the strong Irish side ran out thoroughly convincing winners.
Gretna manager Rowan Alexander retained the starting 11 responsible for the 6-0 weekend thrashing of Hamilton Accies.
Derry were minus Killian Brennan, though Kevin Deery, Gary Beckett and Stephen O'Flynn were all passed fit.
The Irish side started strongly but an error from goalkeeper David Forde let in McGuffie, whose shot fell wide.
McGuffie got it right in the 12th minute though, pouncing on Brendan McGill's header to send a low left-foot shot into the corner of the net for Gretna's first ever European goal.
Derry were back on level terms mid-way through the half when Sean Hargan collected a long ball on the left and sent in a cross for Kelly to beat Alan Main with a hanging header.
Gretna's Chris Innes was booked shortly after the break for a trip on Ciaran Martyn and from the resultant free-kick Deery blasted a superb finish into the top corner of Gretna's net.
Deery had the ball in the back of the net again two minutes later when he fired a ferocious half-volley past the helpless Main from 35 yards.
The Gretna goalkeeper was beaten again after 63 minutes when Martyn raced into the box, rounded Main and squeezed a successful shot between two defenders in the goalmouth.
Martyn then rounded off the rout with his second to virtually assure Derry's progress in the Uefa Cup and leave Gretna stunned.
Gretna: Main, Canning, Innes, Townsley (Jenkins 58), McGill (O'Neil 45), McGuffie, Tosh, Skelton, McQuilken, Deuchar (Graham 74), Grady.
Subs Not Used: Mathieson, Birch, Nicholls, MacFarlane.
Goals: McGuffie 12.
Derry City: Forde, McCallion, Hargan, Hutton, Martyn, Beckett (McGlynn 83), McHugh, Deery, Barry Molloy (Higgins 76), O'Flynn (McCourt 72), Kelly.
Subs Not Used: Jennings, Delaney, Oman, Farren.
Goals: Kelly 22, Deery 54, 56, Martyn 63, 75.
Ref: Marijo Strahonja (Croatia).