The Scarlets were left to rue wasted opportunities as their Heineken Cup campaign started with a home defeat.
HEINEKEN CUP POOL 3
Scarlets (6) 6
Pens: Thomas (2)
Toulouse 6 (9)
Pens: Elissalde (3)
Arwel Thomas and Barry Davies should have passed instead of going for the try line early in the first half of a match which the home side dominated.
Thomas scored all the Scarlets' points with the boot, but the fly-half also missed three relatively easy attempts.
Toulouse hardly troubled the Scarlets defence, but Jean-Baptiste Elissalde's three penalties proved enough to win.
Thomas and Davies were denied in quick succession by some desperate Toulouse tackling as the Scarlets started the game brightly in damp conditions at Stradey Park.
Both went for the score after throwing dummy passes instead of using obvious overlaps, and that was the closest either side came to scoring a try.
Toulouse, European champions in 1996 and 2003, hardly touched the ball as the Scarlets dominated early possession.
But a rare foray into the Scarlets' half yielded a penalty which Elissalde converted to equalise Thomas' fifth-minute effort.
Their first period of sustained pressure came minutes before the interval, and ended with a second Elissalde penalty.
The Scarlets were soon back level, though, as Thomas - who had hit the post with his first penalty attempt - punished more Toulouse indiscretion.
The pattern of the first half continued after the break with the Scarlets controlling possession but failing to make the crucial breakthrough.
Toulouse's penalty count was rising steadily - and prop Omar Hassan was sent to the sin bin on the hour mark as the referee finally lost patience - but Thomas twice wasted relatively simple opportunities to add to his side's advantage.
Elissalde was less wasteful, though, and his third penalty put Toulouse three points ahead with some 20 minutes to go.
Back came the Scarlets again, but it was replacement Gareth Bowen who this time hit the post from a straightforward penalty attempt.
That proved to be their last chance and the Scarlets were left to ponder a match they should have won.
Scarlets: B Davies; G Evans, M Watkins, M Taylor, T Selley; A Thomas, D Peel; I Thomas, M Rees, J Davies, V Cooper, C Wyatt, D Jones, S Easterby (capt), S Quinnell.
Replacements: P John, C Hawkins, A Jones, G Thomas, M Phillips, G Bowen, S Finau.
Toulouse: C Poitrenaud; G Thomas, Y Jauzion, F Fritz, C Heymans; F Michalak, J Elissalde; J Poux, Y Bru (capt), O Hassan, T Brennan, F Pelous, J Bouilhou, C Labit, I Maka.
Replacements: W Servat, P Collazo, G Lamboley, J Fiorini, J Dubois, V Clerc, N Jeanjean.
Referee: Chris White (England)