Plymouth's Sky Bet League Two automatic promotion bid faltered as they suffered a 1-0 home defeat against mid-table Luton.Jack Marriott scored a superb 28th-minute winner, beating home goalkeeper Luke McCormick at his near post following a brilliant reverse pass from Paddy McCourt which wrong-footed the Argyle back line.Marriott - who went agonisingly close with a late second-half angled shot - scored from 12 yards with a measured drive to clinically crown McCourt's mazy run through the home defence.Faltering Plymouth had their two best spells either side of half-time.Playmaker Graham Carey had his shot 42nd-minute shot well saved by Jon Mitchell, who then did well to push over a dipping 30-yard effort from Carey seconds later.Luton somehow managed to keep the ball out during the intense spell of pressure that followed in first-half stoppage time as Curtis Nelson's goal-bound shot was blocked with Mitchell beaten.Glen Rea missed a sitter three minutes into the second half as McCormick spilled the ball and it fell to the Luton central midfielder.Mitchell turned winger Gregg Wylde's far post shot on to the post following Oscar Threlkeld's deep cross from the right.