Ballinamallard United beat Linfield at Windsor Park for the second time this season thanks to Ryan Campbell's goal in the 49th minute.
The goal came after good work down the right by Chris Curran who cut the ball back for Campbell to shoot past debutant Blues keeper Gareth Deane.
Curran had a chance to make it 2-0 but put his lob wide of the target.
United keeper James McGrath did well to save from Philip Lowry and Brian McCaul headed over from the resulting corner.
In the first half, Linfield youngster Conor McMenamin hit a post with an overhead kick.
It was Ballinamallard's first win in six league fixtures and lifts Whitey Anderson's men above Coleraine and into fifth place in their maiden Premiership season.
For Linfield, it was a fourth home defeat of the season but David Jeffrey's side are assured of finishing third as fourth-placed Glentoran remain six points behind them with just one match left.
"To get six points here is remarkable for the team - but we are worthy of it," said Ballinamallard manager Whitey Anderson.
"We have been good defensively and I think this was our 16th clean sheet of the season.
"But we have been good all over the park."