Welsh rugby regions Cardiff Blues and Ospreys lost as their pre-season campaigns began while Dragons won their opening friendly.
Blues, with Wales wing Tom James back after battling depression, lost 17-15 to Leicester Tigers at the Arms Park.
Wales and British and Irish Lions fly-half Dan Biggar played a part for new club Northampton as they beat his former team Ospreys 26-13 in Bridgend.
Dragons won 31-17 at English Championship club Ealing Trailfinders.
Scarlets return to action on Saturday, 18 August when they host Bristol at Carmarthen Park.
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