World number one Lee Westwood was beaten 1up by Ryder Cup team-mate Ian Poulter in the last 16 of the World Match Play Championship in Spain.
Westwood was two down after 12 holes and although he made it all square, Poulter birdied the 17th and held on.
World number two Luke Donald was two down with three to play against Johan Edfors but won at the first extra hole.
In the all-Northern Ireland encounter, Graeme McDowell was three up after eight against Rory McIlroy and won 3&2.
McIlroy was again frustrated on the greens, three-putting on the eighth, and angrily kicked his ball into the bushes after missing a birdie chance on the 12th which saw him remain four behind.
He won two holes in succession but McDowell closed out the match at the 16th with his seventh birdie of the round.
Asked about playing against a close friend McDowell said: "It's hard but you've got to leave your friendship on the sidelines. There were a lot of birdies and it was great to win a quality match."
Westwood, who made seven birdies, struck a superb shot into the heart of the green at the par-three 17th but it was eclipsed by Poulter's tee shot, which rolled round from the fringe at the top of the putting surface and finished within three feet of the cup.
The 35-year-old holed the putt and secured the match after both players birdied the closing par-five.
"He didn't hit a great shot at 17. He wasn't aiming at the left fringe and it comes down to two-foot. You have those days," Westwood lamented.
"You know he's not going to hit it great, but he's going to make a lot of putts and get up and down from everywhere.
"I didn't make any putts, he did and he had a couple more breaks than me. That's the frustrating thing about match play and especially 18-hole match play - sometimes it's not reflective of how the players are playing."
Donald made birdies at the 16th and 17th and after both players birdied the par-five last, the match went to extra holes, beginning at the par-three 10th.
The Englishman put his tee shot into the bunker but played a fine escape to within two feet and a par was good enough after the Swede took four.
Last 16 results (seedings in brackets):
(3) Martin Kaymer (Ger) bt (22) Soren Kjeldsen (Den) 3&2
(19) Noh Seung-yul (Kor) lost to (11) Alvaro Quiros (Sp) 1hole
(18) Ross Fisher (Eng) lost to (7) Charl Schwartzel (SA) 1hole
(4) Graeme McDowell (NI) bt (5) Rory McIlroy (NI) 3&2
(2) Luke Donald (Eng) bt (23) Johan Edfors (Swe) at 19th
(17) Aaron Baddeley (Aus) lost to (8) Francesco Molinari (It) 3&2
(20) Jhonattan Vegas (Ven) lost to (21) Nicolas Colsaerts (Bel) 1hole
(1) Lee Westwood (Eng) lost to (9) Ian Poulter (Eng) 1up