Graeme McDowell bowed out of the WGC-Accenture World Match Play as he went down 3 &2 to Korean YE Yang.
Ireland's US open champion had come from behind in his first two games and threatened to do the same when he took the ninth and 10th to level.
But Yang, the player who beat Tiger Woods head-to-head in the 2009 US PGA Championship, went away from him again and sealed victory with a chip-in birdie at the 16th.
‘It feels great to win over Graeme,’ said Yang. ’I think my overall condition is good, and just because I won today, my condition feels better.’
Long-hitting American Bubba Watson became the first player to reach the quarter-finals of the after crushing Australian Geoff Ogilvy 6&4.
British world number nine Luke Donald ended the fairytale run by teenager Matteo Manassero, beating the Italian 3&2, while pony-tailed Spaniard Miguel Angel Jimenez hammered American Ben Crane 7&6.
In the penultimate match of the day, German world number two Martin Kaymer came from two down after two holes to beat American Hunter Mahan 2&1 in a closely fought encounter.
Watson, making his debut this week in the elite World Golf Championships (WGC) event, charged three up on Ogilvy after just three holes before sealing victory at the par-four 14th.
Ogilvy, a double Match Play champion, conceded the match to his opponent after taking three shots to reach the 14th green on a sun-baked afternoon at Dove Mountain's Ritz-Carlton Golf Club.
Watson, who was effectively eight under par for the first 13 holes, had struck a superb approach there to just under four feet.
‘I hit a lot of good putts, a lot of good iron shots,’ Watson told reporters after booking a place in the last eight against compatriot J.B. Holmes, who beat Australian Jason Day one up.
‘I haven't missed that many fairways, probably no more than five all three days. So it's been good so far, and I've won every time.’
Kuchar never trailed in his match against U.S. Ryder Cup team mate Fowler, going three up after 12 holes before clinching the win at the par-four 17th.
Fowler had reached the third round with a crushing 6&5 victory over world number five Phil Mickelson but the 22-year-old ran out of steam against the rock-steady Kuchar.
‘I think I'm lucky I didn't run into him yesterday,’ a smiling Kuchar said. ‘It sounded like yesterday he was on fire and would have cleaned me out.’
