World number two Luke Donald defeated Masters champion Charl Schwartzel to book a semi-final with Martin Kaymer at the World Match Play Championship.
Donald moved ahead at the ninth and had seven birdies beating Schwartzel 2up.
World number three Kaymer had five birdies and an eagle to win 2up against local hero Alvaro Quiros in Andalucia.
Ian Poulter, who earlier beat top seed Lee Westwood, recovered from two down to oust Francesco Molinari and faces Nicolas Colsaerts in the last four.
Poulter had only four holes to overturn his deficit but won three in succession with three consecutive birdies.
The world number 22 looked set to go three down with three to play at the 15th but holed a clutch putt and secured the match when Molinari could only make par at the last and the Englishman was conceded a fourth successive birdie.
Donald beat then world number one Kaymer in the final of this year's WGC Match Play event in Arizona in February and is now unbeaten in 10 successive matches in the format.
Following Westwood's defeat against Poulter, Donald would need to win the tournament to become world number one for the first time, while Kaymer could regain top spot if he were to claim the title.
Colsaerts, who beat Retief Goosen and Sergio Garcia on Friday and edged out Venezuelan Jhonattan Vegas on the final hole in the last 16, won three holes in succession to overturn an early deficit and move two up after five against Graeme McDowell.
Belgian Colsaerts, who began the week 108th in the world rankings, saw McDowell level the match at the 10th but then won consecutive holes and closed out the match by halving the 17th in par threes.
Poulter, who won the WGC Match Play title in 2010, was delighted with his display and said: "Match play has come at the right time for me. I'd been in poor form. But this is just you against your opponent and hitting the right shot at the right time."
Donald also had a lucky escape, although his came in the last 16 against Johan Edfors.
In the quarter-final he dropped only one shot and after losing the fourth to a birdie, immediately levelled the match at the next and was never behind again.
"It was a lot better than in the morning," he said. "I re-focused and found extra strength. Healthwise I didn't feel 100% and found it hard to concentrate. I kind of got away with it in the morning.
Looking ahead to his eagerly anticipated encounter with Kaymer, the 33-year-old said: "He's played some excellent golf this year and I'm sure it will be a close one."
Quarter-final results (seedings in brackets):
(3) M Kaymer (Ger) bt (11) A Quiros (Sp) 2up
(4) G McDowell (NI) lost to (21) N Colsaerts (Bel) 2&1
(2) L Donald (Eng) bt (7) C Schwartzel (SA) 2up
(9) I Poulter (Eng) bt (8) F Molinari (It) 2up