Samoa piled further misery on Wales with another dramatic win in Cardiff to apply even more pressure on interim coach Robert Howley.
Having lost to Argentina, Howley demanded a reponse from his players.
They were better, but still no match for the islanders for whom Fa'atoina Autagavaia, George Pisi and Johnny Leota scored tries.
Ashley Beck scored a long-range Wales intercept and Leigh Halfpenny's boot added the rest of their points.
The loss meant a fifth successive defeat for Wales, their worst run since 2010, all inflicted since Howley assumed temporary responsibility from 2013 British and Irish Lions coach Warren Gatland.
It was also their third defeat by the Islanders in Cardiff and the first outside a World Cup, to leave Wales with a 5-4 win record against them.
The hosts had every reason to be nervous ahead of this encounter. The 26-12 defeat by Argentina that kicked off their autumn campaign was a reminder of the slumps that followed their 2005 and 2008 Grand Slams.
Another slump, this time post-2012 Six Nations success, is now upon Welsh rugby.
Ahead of this latest upset former captain Paul Thorburn criticised Howley, while another former Wales skipper, Jonathan Davies, reflected the nation's mood with his view that the pressure was on them for Samoa's visit.
And if Wales needed any more reason to feel unsettled in the build-up, the big-screen replay of Dan Biggar throwing an interception pass to Seilala Mapasua in the November 2009 Cardiff clash, that ended 17-13 to the hosts, provided it.
From the kick-off Wales were also on the back foot. Pisi switched the intended direction of his kick away from the opposing forwards.
George North gathered, but the visitors were soon in possession - and took full advantage of Welsh frailty.
Newcastle Falcons number eight Taiasina Tuifua injected direction to a move that had swung to and fro to break through before Pisi again changed the point of attack, freeing Autagavaia for his run to the line.
Pisi added the conversion to the try, which came after a little more than a minute, leaving Wales with an even more severe test of character than they had taken to the field with.
The visitors went on to dominate the opening period as Wales, as against Argentina, were unable to build momentum or territorial advantage.
Being penalised at breakdowns afflicted both teams, but Pisi twice failed with shots at goal while Halfpenny kept Wales in touch with penalties in the 16th and 28th minutes.
However, in the absence of the nous to work their way into Samoa's 22 for the first time, Wales instead benefited from a slice of luck and well-taken opportunism.
Centre Beck intercepted Pisi's pass and sprinted 75 metres to the line for his first Wales try, and Halfpenny converted for a 13-6 lead.
But after Wales lost Ospreys hooker Richard Hibbard and fly-half Biggar to shoulder injuries, Pisi added some more misery with a penalty, although Howley's side led 13-10 at the break.
Wales engineered a morale boost when, for the first time in 124 minutes of rugby this autumn, they finally played their way into an opposition's 22.
However, a knock-on followed, then a penalty against Wales from the scrum.
And Wales went behind for the second time after Kahn Fotuali'i first stole possession, then stole away down the touchline before sending George Pisi over for a try given by the TMO.
Tusi Pisi was unable to convert and Wales went back in front when Halfpenny sent over a penalty. As the final quarter approached, Tusi Pisi kicked his second penalty and Halfpenny squandered a chance to reclaim the lead for Wales after Samoa transgressed at the restart.
The difference between the sides at this point was two points, but contrast in approach and application had been stark.
Where Samoa attacked by coming from deep and at pace, Welsh attacks had often drifted across field.
And while the visitors were happy to kick for territory as part of their tactical mix, Wales again fell victim to a desire to keep the ball in hand with more than half the length of the field and Samoa's renowned defence in front of them.
It took a high challenge on Ken Owens to give Halfpenny the chance to give his side another slender lead.
But back in front went Samoa after Tusi Pisi penalised Wales for infringing at a scrum in the shadow of their posts.
From the restart Wales were unable to profit from a line-out deep in Samoa's 22 as they were eventually stripped of possession having only achieved a 40 metre crab across field.
Having underlined the strong points of their traditions, Samoa also applied increasing dominance to the scrums.
And when Leota followed up skipper David Lemi's kick ahead, he profited after the ball bounced away from Halfpenny.
Tusi Pisi failed with the conversion, allowing Wales a sniff of a draw, but they could not take it.
Wales: L Halfpenny (Cardiff Blues); A Cuthbert (Cardiff Blues), A Beck (Ospreys), J Roberts (Cardiff Blues), G North (Scarlets); D Biggar (Ospreys), M Phillips (Bayonne); P James (Bath), R Hibbard (Ospreys), A Jarvis (Ospreys), B Davies (Cardiff Blues), I Evans (Ospreys), R Jones (capt), J Tipuric (Ospreys), T Faletau (Newport Gwent Dragons).
Replacements: R Priestland (Scarlets) for Biggar (38), G Jenkins (Toulon) for James (61), K Owens (Scarlets) for Hibbard (18), S Andrews (Blues) for Jarvis (78), L Charteris (Perpignan) for Evans (41), S Warburton (Blues) for R Jones (71).
Not Used: Knoyle (Scarlets), S Williams (Scarlets).
Samoa: F Autagavaia (Northland); P Perez (Eastern Province), G Pisi (Northampton), P Williams (Stade Francais), D Lemi (Worcester, captain); T Pisi (Suntory), K Fotuali'i (Ospreys); S Taulafo (Wasps), O Avei (Bordeaux-Begles), C Johnston (Toulouse), D Leo (Perpignan), F Paulo (North Harbour), O Treviranus (London Irish), M Fa'asavalu (Harlequins), T Tuifua (Newcastle).
Replacements: J Leota (Sale) for Williams (56), J Sua (Tasman) for T Pisi (78), T Paulo (Clermont Auvergne) for Avei (58), J Johnston (Harlequins) for C Johnston (49), J Tekori (Castres) for F Paulo (60), T Foma'i (Haweke's Bay) for Treviranus (70).
Not Used: V Afatia (Agen), R Lilomaiava (Laulii).
Referee: Pascal Gauzere (France)
Assistant Referees: Wayne Barnes (England) Jérôme Garces (France)
TMO: Giulio De Santis (Italy)