Antrim recovered from a four-point deficit and the dismissal of Karl Stewart to set up a Leinster hurling championship clash with Laois after victory over Westmeath
The home side were also reduced to 14-men in the second-half when Derek McNicholas picked up a second yellow, and the result was put beyond doubt moments later when Conor Carson hit Antrim's third goal.
Westmeath led by 1-09 to 1-07 at the break thanks to Niall O'Brien's early goal, but Neil McManus hit back soon after to settle Antrim.
The Saffrons started well against a stiff breeze and held a 0-04 to 0-01 advantage after the opening exchanges.
But O'Brien, who was tightly marshalled by Antrim throughout, hit the net for Westmeath to level matters after ten minutes.
That goal encouraged Brian Hanley's side, but McManus hit back for Kevin Ryan's Antrim soon after for his first goal of the game to keep Antrim in touch at the break.
Westmeath showed brightly after the restart with a sweet point from Eoin Price, and they could have stretched their advantage further but McNicholas saw his penalty turned over the bar after 38 minutes.
And minutes later Westmeath were made to really rue the missed goal opportunity as Antrim scored a penalty of their own through McManus, before further points from Jackson McGreeney and Eddie McCloskey helped ease them to a 2-09 to 1-11 lead after 46 minutes.
It seemed as if Westmeath were handed a route back into the tie when substitute Stewart was red carded moments after his introduction following an incident with a Westmeath defender, but it served to galvanise Antrim, who pulled further clear with three quick points.
Full-forward Carson found the net from close range with 12 minutes remaining to give the Ulster men a 3-12 to 1-11 advantage, as the result seemed a foregone conclusion.
Yet, late on, the Lakesmen hit back as a goal from Tommy Doyle saw them pull to within five points.
However, after McNicholas was sent off after picking up a second booking, Antrim closed out the game with points from subs Shay Casey and Ciaran Clarke to seal a deserved victory.
Antrim: R McGarry; B McFall, A Graffin, M McFadden; C McKinley, N McAuley, P Shiels (0-01); J McGreevey (0-02), T McCloskey (0-01); S Beattie, M Donnelly (0-01), E McCloskey (0-02); S McNaughton (0-05, 0-02f, 0-01'65), C Carson (1-00), N McManus (2-04, 1-00 pen).
Subs: C McGuinness for Beattie (21 mins), O McFadden for M McFadden 39), K Stewart for McGuinness (49), C Clarke (0-01) for Donnelly (58), S Casey (0-01) for McNaughton (64).
Westmeath: P Collins; T Gallagher, A Price, D Fennell; G Greville, A McGrath, T Doyle (1-00); E Price (0-04), R Greville (0-01); J Shaw, D McNicholas (0-05, 0-02f), J Clarke; N O’Brien (1-00), B Murtagh (0-02), A Clarke (0-01).
Subs: C Jordan for A Price (63 mins), J Boyle for J Clarke (66), S Power for Fennell (66).
Referee: J Owens (Wexford).
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