Westmeath produced a fine finish in this Division 3 game at Corrigan Park to turn a five-point deficit into a four-point win over Antrim, but results elsewhere meant it wasn't enough to seal promotion.
The hosts had looked well in control for long stages but were made to pay for some poor finishing as their five-point lead turned into a three-point deficit in the space of 10 second-half minutes.
A dozen wides told its own story for Antrim who will be wondering how they let such a commanding position slip, but when the visitors had their chance to push on, they did in style to run out winners.
John Heslin's penalty proved to be the catalyst for Westmeath who hit an unanswered 1-5 in a 10-minute spell that would put them in the box seat and they never looked like letting it slip in the home stretch.
Antrim opened much brighter and were three up with some fine scores by Conor Murray and Pat Shivers as Westmeath, who lost midfielder Sam Duncan to injury early on, seemed off the pace.
However, the hosts would lose Tomás McCann to the sin-bin on 12 minutes and by the time he returned, Westmeath had drawn level with Nigel Harte getting them on the board.
They also had a couple of goal chances with Sam McCartan denied by Mick Byrne and then Peter Healy made a vital block on Lorcan Dolan.
When McCann returned, Antrim regained the initiative with four points in-a-row, with two of those from Marc Jordan and Dermott McAleese that could have really been goals but they were unable to keep their shots down.
The hosts led 0-8 to 0-4 at the half and extended that gap with Pat Shivers kicking his third of the day just seconds into the second period, with Heslin and Ryan Murray trading points as Antrim looked to be in control despite the wides stacking up.
This game would suddenly flip on its head whenJohn Heslin tucked away a 49th-minute penalty that was awarded after Martin Johnston's foot block on Jonathan Lynam.
This saw Westmeath burst to life as the Antrim kick-out malfunctioned and a further five points put the visitors a goal clear, with Heslin kicking two and Jamie Gonoud forced to settle for a point when Byrne made a magnificent save to tip his shot over the crossbar.
Ryan Murray added a couple of points to keep Antrim in the hunt, but these were cancelled out by Heslin and Luke Loughlin as Westmeath saw the game out with Murray finishing the game in the sin bin after picking up a black card in stoppage time, while Westmeath's Robbie Forde had the final say to put a gloss on the victory.
Antrim: M Byrne; J McAuley, R Johnston, P Healy; D Lynch, M Johnston, D McAleese (0-1); M McCann, K Small; T McCann, M Jordan (0-1), R McCann (0-2f); R Murray (0-3, 1f), P Shivers (0-3), C Murray (0-2, 1 mk).
Subs: P McAleer for Tomás McCann (HT), J Gribin for D Lynch (58), J Laverty for M Johnston (62), O Eastwood for P Shivers (62), E McCabe for M Jordan (64).
Westmeath: J Daly; J Smith, K Maguire, J Gonoud (0-1); D Giles, N Harte (0-1), D Lynch; J Lynam, S Duncan; R Connellan (0-1), R O'Toole (0-1), S McCartan; L Dolan, J Heslin (1-5, 1-0 pen, 0-3f), A Gardiner (0-1).
Subs: K Martin for S Duncan (5), L Loughlin (0-2) for L Dolan (HT), K O'Sullivan for K Martin (64), B Kelly for A Gardiner (70+1), R Forde (0-1) for J Lynam (70+4).
Referee: James Molloy (Galway).