CASARES, Spain, May 19, 2012 (AFP) - Poulter had gone eight games unbeaten in the prestigious tournament but found Spain's Alvaro Quiros in imperious form, going down 4&3, while compatriot and second seed Justin Rose having humbled Open winner Darren Clarke on Friday was hammered 4&3 by Belgian Nicolas Colsaerts.
Poulter refused to blame his defeat on having had his foot run over by a golf buggy earlier in the week.
"I don't need excuses," said Poulter.
"I had plenty of chances and didn't take them - simple. I just didn't play good enough."
Joining Quiros and Colsaerts in the quarter-finals later on Saturday are Northern Ireland's former US Open champion Graeme McDowell, who has a mouthwatering clash with dashing Spaniard Sergio Garcia, after beating unheralded Englishman Richard Finch.
Scotland's rejuvenated 1999 Open champion Paul Lawrie, who looks set for a return to the European Ryder Cup team this year after a 13 year hiatus, strolled to an impressive 5&4 thrashing of veteran Dane Thomas Bjorn.
He will play South African star Retief Goosen - who beat England's Robert Rock - for a place in the semi-finals.
Garcia, who has like Lawrie shown a return to a semblance of the form that had him up at the top of the world elite until suffering a slide in form three years ago, beat promising English youngster Tom Lewis, winner of his maiden EPGA title in only his third tournament last year's Portugal Masters, 4&3.
World Match-Play Championship scores on Saturday:
Last 16
Retief Goosen (RSA) bt Robert Rock (ENG) 3 & 2
Brandt Snedeker (USA) bt Camilo Villegas (COL) 3 & 2
Nicolas Colsaerts (BEL) bt Justin Rose (ENG) 4 & 3
Alvaro Quiros (ESP) bt Ian Poulter (ENG) 4 & 3
Graeme McDowell (NIR) bt Richard Finch (ENG) 3 & 2
Sergio Garcia (ESP) bt Tom Lewis (ENG) 4 & 3
Paul Lawrie (SCO) bt Thomas Bjorn (DEN) 5 & 4
Rafael Cabrera-Bello (ESP) bt Robert Karlsson (SWE) 1 up