The Faithful County came out on top despite an early red card.
Offaly struck a potentially fatal blow to Westmeath's championship hopes on Saturday.
Both counties needed victory after losing their opening Joe McDonagh Cup rounds last time.
It was Johnny Kelly's side that came out on top after an eventful contest that saw Jason Sampson red carded after 30 seconds, and a goal for both sides in the opening five minutes.
A late Dan Bourke goal eventually sealed a crucial victory for the Faithful County.
Killian Doyle led the scoring for the Lake County with 15 points, while Brian Duignan's 1-11 proved decisive for Offaly.
The final score was 2-23 to 1-20.
Kelly says Offaly will be appealing Sampson's red card.
He says says he's proud of his players,
Elsewhere in the Joe McDonagh, Laois continued their march to the final with a massive win over Meath 7-29 to 1-16.
While Kerry backed up their win over Westmeath last time out with a 26 point to 2-12 win over Down yesterday.
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