A late goal from John Owen secured maximum points for second-bottom Aberystwyth.
Saints had won 10 and drawn two of their opening 12 league games this season, but their unbeaten record came to an end at Park Avenue after Owen struck in the 84th minute.
TNS travelled to Aberystwyth having scored 11 unanswered goals in winning their two previous league games against Cardiff Metropolitan University 5-0 and Haverfordwest County 6-0.
But they were unable to find a way through against the home side, with Anthony Limbrick’s team now six points clear of Flint Town United at the top of the table.
Saints went in search of an early breakthrough and Louis Robles was denied by a good save from Gregor Zabret.
Aberystwyth goalkeeper Zabret then pushed away a long-range effort from Ryan Brobbel.
The home side went close when Owen volleyed over the crossbar from close range just before the half-hour, before Brobbel headed over for the visitors at the other end.
Saints continued to push for a goal in the second half, with Danny Davies lifting a shot over the crossbar and then Redmond forced a save from Zabret.
Substitute Adrian Cieslewicz, set up by Declan McManus, fired just wide shortly before Owen scored the decisive goal for Aberystwyth.
Saints are next in action when they face Newtown at Park Hall next Friday, November 19 (7.45pm).
TNS: Harrison, D. Davies, Hudson, Astles, Marriott, Clark (Cieslewicz), Routledge, Redmond, Brobbel, McManus, Robles (J. Williams). Subs not used: Ebbe, Smith, Baker, Canavan, Parry.