Despite recovering from two goals down the Robins squandered a second half lead as defeat in the Mid Wales derby brought the season to a close.
Aber found themselves two in front through John Owen and Declan Walker, before Ethan Jones continued his hot run of form just before the break.
Nick Rushton then levelled things up, before a super Ryan Kershaw strike turned the tables.
But the tide turned again as Ryan Wade headed Aber level, before Matthew Jones popped up to give his side an 85th minute lead.
Wade fired home again in stoppage time leaving the Robins bemused how they had lost the game from such a commanding position.
The Robins were looking for a winning end to their campaign, but it almost began horribly after ten minutes.
Tom Goodwin, slotting in at the back in place of the suspended Kieran Mills-Evans was shepherding a ball back to Dave Jones.
However as Jones went to collect Joe Phillips nicked the ball off him, but the referee blew for a free kick to deny Aber a certain goal.
Chris Hughes’ men cut the Aber backline open with a few neat moves that came to nothing, before a spectacular but albeit controversial goal gave them the lead.
Craig Williams and Owen battled on the left touchline, and Williams and the Robins players certain it had gone out and stopped, awaiting the linesman’s flag.
However it never came and from a tight angle former Caersws man Owen lifted the ball over Jones and into the net.
Robins players, led by Williams and Alex Fletcher protested profusely to the officials but to no avail, with the latter receiving a yellow card for dissent.
Tom Owens then had a volley saved, before the Robins came with millimetres of levelling the scores.
Callum Roberts’ free kick beat Chris Mullock in the Aber goal, hit the post and somehow came back out and away to safety.
The Robins had really failed to kick into gear and it was Aber who looked dangerous coming forward.
Wade headed inches wide from a Joe Phillips cross on the half hour mark, as the home side looked to increase their lead and build momentum ahead of next week’s Welsh Cup final.
Ryan Kershaw saw a speculative effort go wide, before he conceded possession in his own third which led to Aber increasing the lead.
He turned one to many times and was robbed of the ball, which was played through to Walker who beat Goodwin on the by-line before smashing it past Jones and in off the post.
The Robins almost replied immediately as Rushton found Jones, but the inform forward was denied by Mullock’s feet.
However the striker wasn’t to be denied in first half stoppage time, as he tucked home his sixth goal in five starts.
Damien Allen, usually very clinical in possession gave the ball away and Jones capitalised as he cut in and fired past Mullock.
Just seven minutes of the break the Robins really should have been level and Jones should have made it back to back braces.
He was slipped through but could only fire wide when one on one with Mullock.
However two minutes later his strike partner made up for it as the Robins drew level.
A ball found Rushton who fended off two defenders before firing into the corner with the aid of a deflection.
Jones almost turned the match on its head as he curled wide seconds later, before the Robins did complete the turnaround on the hour mark.
Kershaw looked for a pass on the edge of the box, but instead curled a dipping shot past Mullock and in.
It should have been four soon after but Neil Mitchell passed up a great chance.
Kershaw’s through ball some him one on one with Mullock, and he squared for Rushton but the ball came straight back to him before he blazed over.
Chances were coming and going for Newtown, as 15 minutes from time Jones found Rushton but he blasted is effort off the crossbar.
It was starting to feel like the Robins were going to regret not taking their second half chances, and that is exactly what happened soon after.
First Jones produced a top save to deny Jack Rimmer, then in the same passage of play Phillips crossed for Wade to glance a header home.
Then two minutes later Aber had turned the tables on the Robins and found themselves in front with ten minutes remaining.
Jones could only parry Phillips’ long range effort, and Jones was there to follow it in.
As Newtown pushed forward, they were bound to leave gaps and that told late on as with a minute to do Wade fired past Jones to give his side the win.
After being 3-2 with 25 minutes to play it was hard to see how Newtown lost that game, but not taking chances again proved to be the downfall.
Aber – Mullock, Walker (Borrelli 58), Wollacott, Melvin (Sherlock 42), Owens (Rimmer 58), Owens, Wade, Jones, Young, Allen, Phillips
Subs not used – Kersh, Kellaway, Walters
Robins – Jones, Williams, Denny, Sears, Roberts (Harries 81), Fletcher, Goodwin, Kershaw, Rushton, E Jones, Mitchell (Kenton 81)
Subs not used – Perry, C Williams, , Evans, Boundford