The Scarlets, Ospreys and Dragons were all beaten in pre-season tour matches against French sides on Friday, in the build-up to the Pro12 season.
Ospreys fielded a mix of youth and experience but lost 49-25 to a full strength Clermont Auvergne team.
And the Dragons suffered a heavy defeat to Biarritz, with former wing Aled Brew scoring two tries in a 40-3 loss.
Scarlets, who also included Wales under-20 players Kirby Myhill and Samson Lee, took an early lead against Narbonne through winger Andy Fenby's unconverted try.
Fullback Dan Newton kicked a second-half penalty but Narbonne secured the win with an interception try five minutes from time.
Kahn Fotuali'i, Ross Jones and Matthew Morgan all crossed the whitewash for Ospreys at Clermont, with Morgan converting twice and kicking two penalties, but the home side hit back with seven converted tries, including two each from Sitiveni Sivivatu and Noa Nakaitaci.
Former Dragons wing Brew turned on his former team mates with two tries for his new club Biarritz at the Parc des Sports Aguilera.
The visitors conceded six tries on a difficult evening in front of 7,000 Basque supporters, with Ngwenya, Lesgourges, Lakafia and Van Staden all crossing.
Cardiff Blues lost 25-30 to Worcester Warriors at the Arms Park on Saturday, with an Andy Goode penalty the difference between the sides.
Tom Williams scored a hat-trick for Blues but the visitors hit back with tries from Taulava, Pennell and Frost.
The Dragons round off their pre-season friendlies at home to London Irish, while Ospreys take on Bath at the Liberty Stadium.
Scarlets complete their summer preparations with a trip to Worcester Warriors and a home game against London Welsh.