* Oosthuizen crushes Simpson 5&4
* McDowell outlasts Mahan over 21 holes
* Furyk rallies to beat English one up (Adds McDowell quotes, detail)
Feb 21 (Reuters) - South African Louis Oosthuizen coasted in sizzling style while Americans Jim Furyk and Rickie Fowler both staged thrilling comebacks to reach the WGC-Accenture Match Play Championship quarter-finals in Marana, Arizona on Friday.
Also advancing into the last eight were Frenchman Victor Dubuisson, making his debut this week in a World Golf Championships event, and Northern Irishman Graeme McDowell, after a third successive Houdini-like escape at Dove Mountain.
Former British Open champion Oosthuizen, who upset top-seeded Swede Henrik Stenson in the previous round, was a flawless six under for the day when he sealed a commanding 5&4 victory over American Webb Simpson.
Oosthuizen, who has been one of the standout players all week, eagled the par-five second and then added four birdies to tighten his grip on the third-round encounter.
"I'm playing some of my best (golf) now," Oosthuizen told reporters. "I'm hitting the ball really good and just need to make the putts.
"I made quite a few birdies coming in, and he put himself in a few tough spots off the tee to make bogeys and pars. My golf has been really solid."
Oosthuizen will next meet Australian Jason Day, who never trailed on the way to a comfortable 3&1 win against South African George Coetzee.
PGA Tour veteran Furyk and emerging talent Fowler also reached the last eight, but both had their work cut out before they advanced.
Furyk came from three down after six holes to win a hotly contested match with compatriot Harris English one up, making sure of the win with birdies at 16 and 17 before recording a matching par at the 18th.
"Just steady play," said Furyk, 43, after reaching the last eight for the first time in 14 starts at the elite WGC event. "I really hit a lot of greens, a lot of fairways, gave myself a lot of opportunities.
"It was a tough match. He played real well early on and I played real well, chipped in on 18 and that's what gave me the one-up victory."
Fowler, who upset 2010 champion Ian Poulter and in-form American Jimmy Walker in his first two matches, rallied from three down after eight holes to pip Spaniard Sergio Garcia one up.
The American piled up five birdies in the last 10 holes to seize control and will take on Furyk in Saturday's quarter-finals.
"I knew I had my work cut out for me, and I gave it the best fight I could," said Fowler. "We've had a lot of fun playing together. We did out there today, as well."
McDowell, taken to 19 holes in his opening match and 18 in his second as he had to rally in both, came from two down after 16 holes to edge American Hunter Mahan after 21.
The Northern Irishman won the 17th and 18th, sank a 20-footer for par at the 20th to stay in the match and then sealed his third remarkable victory this week with a birdie at the 21st.
"I really don't know what to say," former U.S. Open champion McDowell said after emerging triumphant in a re-match of his decisive singles clash with Mahan at the 2010 Ryder Cup, also won by the Northern Irishman.
"Obviously I'm holing some very important putts that I really can't give my normal reactions to, because I can scarcely believe what's going on. I'm not embarrassed, but I just feel like I'm robbing these guys."
McDowell will next meet Dubuisson, who beat former Masters champion Bubba Watson one up in an erratic match that featured just six birdies between them.
Jordan Spieth, 20, ousted fellow American and defending champion Matt Kuchar in a match of high quality, completing a 2&1 victory with his ninth birdie of the day at the par-four 17th.
Veteran South African Ernie Els, who edged second-seeded Englishman Justin Rose after 20 holes in the previous round, beat PGA Championship winner Jason Dufner one up and will next take on Spieth, an opponent less than half his age. Els is 44. (Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Gene Cherry/Greg Stutchbury)