The Scarlets were comfortably beaten by Ulster in their European Champions Cup clash on Saturday night.
The Irish side earned a bonus point, with tries from Darren Cave, Ruan Pienaar, Tommy Bowe and Rory Best.
Rhys Priestland kicked three penalties for the Scarlets, who had James Davies and Liam Williams sent to the sin bin.
The defeat leaves the Welsh side in a difficult position in Pool 5,ahead of the return fixtures at Parc y Scarlets next weekend.
The Ospreys fought back valiantly in the second half to claim a 19-19 draw against French side Racing Metro in the European Champions Cup.
The hosts trailed 16-6 at half-time at the Liberty Stadium, but Dan Biggar kicked two penalties to narrow the scores. Johannes Goosen's drop goal put Racing Metro 19-12 ahead with just eight minutes left, but the Welsh side found a thrilling response.
Flanker Justin Tipuric broke clear, and his pass found Rhys Webb, then Josh Matavesi to touch down. Biggar kicked an easy conversion to take his tally to 14 for the afternoon.
With the scores locked together, it was a nervy last few minutes, but the draw means the Ospreys are still in with a chance in Pool 5.
Cardiff Blues pulled away from London Irish with two second-half tries in their European Challenge Cup clash.
Scrum half Lloyd Williams touched down in the corner just after the hour, after Cory Allen was held up just short of the line.
Substitute hooker Kristian Dacey then crossed the line after relentless pressure from the Blues forwards.
The visitors scored a late penalty try of their own, to make the final score at Cardiff Arms Park 24-14.
The Blues have now won all three of their games in the European Challenge Cup.
The Blues were neck and neck with London Irish at half time in the European Challenge Cup.
Shane Geraghty crossed for Irish after 8 minutes, only for Richard Smith to pull one back for the Blues. New arrival Gareth Anscombe slotted the conversion, but missed a penalty later.
The Ospreys have it all to do in the second half after a powerful Racing Metro had the better of the first period at the Liberty Stadium.
Lock Francois Van der Mewe scored the only try of an opening half which also saw Osprey James King sent to the sin bin.
Wales outside half Dan Biggar kicked two penalties for the Ospreys.
Newport Gwent Dragons got Wales' weekend of European rugby off to a winning start, seeing off their Romanian opponents 37-10 in Bucharest.
Despite finding themselves 10 - 0 down early on, five tries were enough to secure a bonus point win for the Welsh team.
Ashley Smith, T Rhys Thomas and James Thomas all touched down, while Andrew Coombs got two.
Glasgow Warriors reclaimed a top-four place in the Guinness PRO12 after a hard-fought 19-15 victory over Newport Gwent Dragons at Scotstoun.
Having lost to Scarlets in the last round of games, it was not a spectacular response from Glasgow whose coach Gregor Townsend will know his men must play better to mount a serious challenge for the silverware this season.
If the Welsh visitors had capped a spell of sustained pressure in the closing 10 minutes, there could have been few complaints in the home camp.
Glasgow's points came from a penalty try and a 14-point contribution with the boot by Duncan Weir.
For the Dragons, who now sit second from bottom, Geraint Rhys Jones landed five penalties in an immaculate kicking performance.
Scrum-half Rhys Webb believes Wales have given themselves "a good springboard" for the RBS 6 Nations Championship after ending six years of hurt against major southern hemisphere opposition.
A 12-6 victory over South Africa was their first success against the Springboks for 15 years, and only a second since fixtures began between the countries in 1906.
It also ended a run of 22 defeats in a row at the hands of South Africa, New Zealand and Australia, giving Wales a major send-off into their Six Nations opener on February 6 when England arrive at the Millennium Stadium.
Full-back Leigh Halfpenny's four penalties sunk South Africa.
"This win has been there waiting for us.
"We are just happy to pick it up, and we will go back to our regions now and hopefully come out firing for the Six Nations. It's definitely a good springboard.
"We targeted the four games (in the autumn series), but we slipped up against Australia and New Zealand in games that we could have won. Everyone was positive after the performance against New Zealand, and we took it into the game with South Africa and came away with a victory.
"We will learn a lot from the campaign, particularly in respect of playing for the full 80 minutes. That's the big thing for us, playing and concentrating for the whole game. We did that against South Africa.
"We slipped up against Australia and New Zealand, but to be fair, we haven't been far away in those games. We pushed New Zealand for 69 minutes last week, and to finally get that win against one of these teams feels pretty special."
Webb and his half-back partner Dan Biggar were arguably Wales' star performers of the past month, and it is a combination that will be integral to Welsh hopes of Six Nations and World Cup success next year.
Webb scored tries against Australia and New Zealand, while Biggar saved his best until last, delivering a man-of-the-match display that was built on defensive courage and tactical appreciation.
Wales coach Warren Gatland says he couldn't bring himself to watch as the clock ran down just before his side's win yesterday.Read the full story ›