Fly-half Stephen Jones orchestrated the Scarlets' recovery
Saints: (14) 14
Tries: C Spencer 2.
Con: R Kydd 2.
Scarlets: (10) 22
Tries: G Evans, M Thomas, C Stuart-Smith.
Con: C Thomas, S Jones.
Pens: C Thomas.
Llanelli Scarlets produced a dominant second-half display to win a tough pre-season encounter at Northampton.
A Carlos Spencer brace of tries, seizing on two Welsh handling errors, both converted by Robbie Kydd, gave Saints a 14-10 half-time lead.
But a completely changed Scarlets XV after the break reaped tries for Martyn Thomas and Clive Stuart-Smith, adding to Garan Evans' first-half effort.
Saints hooker Steve Thompson and John Davies were sin-binned for fighting.
The game was punctuated by further outbreaks of hostilities, causing referee Rob Debney to give opposing skippers Thompson and Simon Easterby a stern lecture.
Wales and Lions fly-half Stephen Jones was the chief architect for the Scarlets' revival after his half-time introduction, a welcome returnee after his time in French rugby with Clermont Auvergne.
Saints: Rob Laird; David Akinluyi, Chris Wyles, Robbie Kydd, Ben Cohen; Carlos Spencer, Ian Vass; Simon Emms, Steve Thompson (capt), Pat Barnard, James Percival, Matt Lord, Paul Tupa, Darren Fox, Mark Hopley.
Replacements: Dan Richmond, Soane Tonga'uiha, Chris Budgen, Christian Short, Alex Rae, Mark Robinson, Luke Myring, Paul Diggin.
Scarlets: Garan Evans; Dafydd James, Regan King, Gavin Evans, Darren Daniel; Ceiron Thomas, Dwayne Peel (capt); Phil John, Ken Owens, John Davies, Lou Reed, Scott Macleod, James Bater, Gavin Thomas, Nathan Thomas.
Replacements: Iestyn Thomas, Matthew Rees, Dominic Day, Alix Popham, Clive Stuart-Smith, Stephen Jones, Mark Jones, Matthew Watkins, Simon Easterby, Adam Jones, Inoke Afeaki, Deacon Manu, John Davies, Martyn Thomas, Alec Jenkins.