Cavan achieved their goal after a real war of attrition in a derby duel at rain-lashed Kingspan Breffni Park.
The Breffni men won pulling up to retain their Division 2 status for another year. Westmeath failed to score for a full 40 minutes after a bright start albeit against the wind and now face a relegation battle.
The Blues hadn't scored a goal in the entire current NFL but Brendan Fitzpatrick's 44th-minute effort worked the oracle and left Westmeath staring at a relegation dogfight.
Cavan were caught napping early on though with Kieran Martin finding the net for the visitors after a great delivery from Callum McCormack in the seventh minute.
Tom Cribbin's side almost broke through for a second goal in the 15th minute but Cavan livewire Jason McLoughlin made a great interception to deny Shane Dempsey a clear shot.
Cavan took 14 minutes to add to Niall McDermott's opener for his side and it was a free from Martin Dunne (below) which helped to up the ante. The home team finished the first half with a spring in their step and a fine McDermott point helped get his side on level terms, 0-4 to 1-1, at the interval.
The Blues hit the jackpot nine minutes after the restart when Fitzpatrick rattled the Westmeath net after great work by James McEnroe.
A brilliant point from Martin (40) ended a 31-minute barren period for the Leinster men only for in-form midfielder Gearoid McKiernan's brace to seal the deal after Jamie Gonoud (61) saw red after an off-the-ball incident.
Man of the Match: Kieran Martin
Scorers - Cavan: B Fitzpatrick 1-0; G McKiernan, N McDermott (1f), M Reilly (2f), M Dunne (2f) 0-2 each. Westmeath: K Martin 1-2 (1f); J Heslin 0-1.
Cavan - C Gilsenan 6; J McLoughlin 7, R Dunne 7, R Flanagan 6; J McEnroe 7, F Flanagan 8, D O'Reilly 7; T Corr 7, G McKiernan 8; D McVeety 6, N McDermott 6 , M Reilly 8; C Mackey 7, M Dunne 8 , B Fitzpatrick 8. Subs: C Conroy 6 for N McDermott (44); J Farrelly 6 for C Gilsenan (52); N Murray 6 for R Flanagan (63); T Hayes for B Fitzpatrick (66); J Brady for N M Dunne (67).
Westmeath - G Connaughton 6; M McCallon 7, K Maguire 6, G Gonoud 6; K Daly 6, J Gilligan 7, J Egan 6; P Holloway 7, J Heslin 8; P Sharry 6, G Egan 6, K Martin 8; S Dempsey 7, C McCormack 6, L MacGabhann 6. Subs: D Glennon for L MacGabhann (44);D Duffy for P Holloway (52); D McCormack for C McCormack (68).
Ref - J Henry (Mayo)