Dundee United closed to within a point of third-placed Motherwell in the race for a Uefa Cup spot with an easy win.
Garry Kenneth nodded United in front from a corner in the 15th minute, amid the first goalmouth action of the game.
David Robertson and Noel Hunt squandered chances to make it two as Gretna struggled to make any impact.
Morgaro Gomis struck on 51 minutes and then Robertson beat the offside trap to stroke home Christian Kalvenes' cross as United ran out comfortable winners.
The opening stages held little to excite the small crowd of just 501, who were all housed in the main stand at Fir Park.
But Kenneth headed United into the lead amid a goalmouth scramble after the first corner of match in the 15th minute.
Kalvenes' connected with Jim O'Brien's inswinger but his header came back off the bar.
Gretna keeper Greg Fleming spilled the rebound and Kenneth was there to nod home from close range.
The lacklustre hosts won their first corner midway through the half.
Chris Innes' header looped just wide but United keeper Lukasz Zaluska had it covered.
United should have gone further ahead in the 27th minute when Robertson met a Kalvenes cross inside the six-yard box, but he volleyed over the bar.
The low-key game was mainly taking place in the Gretna half.
Mickael Buscher wasted a chance to put United under pressure when he over-hit a free-kick 30 yards out on the touchline.
Gretna improved their possession just before the break, but a 30-yard effort by Brendan McGill that sailed well over summed up their lack of goal threat.
Fleming kept them in the game when he pushed Noel Hunt's low effort wide following a driven cross by Kalvenes.
Gretna brought on the fit-again Paul Murray and Aurelien Collin at half-time for John-Paul Kissock and Nicky Deverdics.
Gavin Skelton came close to the equaliser five minutes into the second half when his low shot from 15 yards was blocked by Zaluska following Rhys Meynell's cross.
But United went straight up the park and scored as Gomis placed Hunt's cutback into the bottom corner after the unmarked O'Brien had taken a fresh-air swing.
A backtracking Fleming pushed Sean Dillon's overhit cross on to the post as United threatened to put the game beyond the Borderers.
O'Brien was booked for diving before Gretna almost earned a lifeline when Brendan McGill beat Zaluska to a loose ball on the edge of the box.
However the winger's shot drifted away from goal and United again broke quickly.
Danny Hall saved the hosts by clearing from the goalmouth after Fleming had parried Robertson's cross.
The third goal was coming though, and Robertson provided it in the 65th minute when he beat the offside trap to side-foot home a Kalvenes cross.
Gretna: Fleming, Barr, Meynell, Innes, Naughton, McGill, Hall, Skelton, Deverdics (Murray 46), Kissock (Collin 46), Buscher (Wilkinson 77). Subs Not Used: Krysiak, Makinwa, Baldacchino, Griffiths.
Booked: Innes.
Dundee Utd: Zaluska, Dillon, Kenneth, Dods, Kalvenes, Robertson, Gomis, Buaben, Flood (Kerr 84), Hunt (Odhiambo 88), O'Brien (Conway 73). Subs Not Used: McLean, Grainger, De Vries, Swanson.
Booked: O'Brien.
Goals: Kenneth 16, Gomis 51, Robertson 64.
Att: 501
Ref: B Winter (Scotland).
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