Samoa handed Wales their fifth consecutive loss with a 19-26 upset at the Millennium Stadium in Cardiff on Friday night.
The victory is Samoa's fourth over Wales and will do the hosts no favours as the Rugby World Cup Champion All Blacks visit Cardiff next week.
The result drops Six nations Grand Slam champions Wales down to eighth in the Rugby World rankings after last week's loss to Argentina and three losses to Australia in June.
Fa'atoina Autagavaia, George Pisi and Johnny Leota all crossed as the Six Nations champions suffered a similar fate to their predecessors.
Memories of famous World Cup shocks from 1991 and 1999 came flooding back as the ferocious tackling and clinical finishing of the visitors rocked hosts Wales.
But unlike those wins of the past, this was far les of a surprise given the mess Welsh rugby suddenly finds itself in following three losses in Australia and defeat last week to Argentina.
Ashley Beck's interception try before half-time handed Wales a 13-7 lead and appeared to have settled home nerves after falling behind to an early try only for second-half scores from Pisi and Leota wrapped up a deserved victory for the Pacific islanders.
Samoa made a dream start with a try little more than a minute into the game that stunned the 44,000 crowd at the Millennium Stadium.
Number 8 Taisasina Tuifu'a made yards after breaking through in midfield. Fly-half Pisi was quick to spread the attack wide where Paul Williams and George Pisi combined to hand full-back Autagavaia a straight-forward finish from close range.
Pisi converted for an early 7-0 lead that was almost stretched further only for the fly-half's penalty to struck the post.
Samoa lived up to their reputation as fearsome tacklers and Wales hooker Richard Hibbard was the first to take the full brunt of the south sea islanders, forced off after just 18 minutes.
It summed up an uncomfortable opening for the hosts who were still reeling from their defeat to Argentina six days earlier.
Wales slowly regained their composure as Halfpenny cut the deficit to a single point with two penalties while Pisi missed a second effort.
Just a minute later and another mistake by Pisi led to Wales taking the lead through Beck.
Samoa were full of ambition as they pressed forward but Pisi's arching pass intended for his brother was easily telegraphed by the Welsh centre who galloped 70 metres up field to score his team's first try of the autumn series.
Samoa ended the half with a Pisi penalty and wasted no time in regaining the lead after half-time with a second try.
Ashley Beck was robbed of possession and Kahn Fotuali'i turned defence into attack, skipping past Jamie Roberts before Pisi finished acrobatically in the corner with a superb piece of individual skill to touch down in mid-air.
Pisi missed the conversion before exchanging a series of kicks with Halfpenny as the lead changed hands five times during the second half.
Leading 21-19, Samoa repelled a rare attack by Wales who, for the second week in a row, failed to show any threat with the ball.
Instead it was Samoa who had the final say when David Lemi kicked ahead, Halfpenny and Autagavaia both missed the bouncing ball to leave replacement Leota to touch down for the match-winning try two minutes from time.
Final Score Wales 19 (13) Samoa 26 (10)
Penalties: Halfpenny 4
Tries: Autagavaia, Pisi, Leota
Penalties: Pisi 3
Leigh Halfpenny; Alex Cuthbert, Ashley Beck, Jamie Roberts, George North; Dan Biggar, Mike Phillips; Toby Faletau, Justin Tipuric, Ryan Jones (capt), Ian Evans, Bradley Davies, Aaron Jarvis, Richard Hibbard, Paul James.
Replacements: Ken Owens, Gethin Jenkins, Scott Andrews, Luke Charteris, Sam Warburton, Tavis Knoyle, Rhys Priestland, Scott Williams.
Fa'atoina Autagavaia; Paul Perez, George Pisi, Paul Williams, David Lemi (capt); Tusiata Pisi, Kahn Fotuali'i; Taiasina Tuifu'a, Maurie Fa'asavalu, Ofisa Treviranus, Teofilo Paulo, Daniel Leo, Census Johnston, Wayne Ole Avei, Sakaria Taulafo.
Replacements: Ti'i Paulo, Viliamu Afatia, James Johnston, Joe Tekori, Tivaini Foma'i, Jeremy Su'a, Johnny Leota, Robert Lilomaiava