Craig Stadler, seeded 57th in this event, also needed an extra hole to defeat Andrew Coltart 1-up, while 55th-seeded Steve Stricker trounced seventh-seed Justin Leonard 6 & 5.
Elsewhere, unheralded Nick O'Hern of Australia, who knocked out second-ranked Hal Sutton in the first round, beat 18th-seeded Dudley Hart to advance to Saturday's quarterfinals.
Also, fourth seed, Tom Lehman lost to Brad Faxon 1-up and 21st- ranked Pierre Fulke upset fifth seed Michael Campbell 1-up. Toru Taniguchi beat Stuart Appleby 2 & 1 and Shigeki Maruyama bettered Mark McNulty 4 & 3 on Friday.
Van de Velde, best-known for his 1999 British Open collapse, had a chance to upset the top seed and took his first lead of the match when he knocked his approach shot at the 16th to within two feet. Els holed a 30-footer at the next hole to square the match. At 18, Van de Velde drained an 18-foot birdie putt, pumping his fist as the ball fell into the cup. Els halved the hole after drilling a six-footer to force extra holes.
Neither man got off the tee well at the first extra hole. Els drove right into the trees and Van de Velde's shot was headed in the same spot until his ball hit a branch and moved sharply left into a bunker. Els played his second shot into a left greenside bunker while Van de Velde played his shot short of the green. Van de Velde made a mistake with his third shot as he chipped it over the green, the hit his fourth to within three feet for his par effort. However, Els' sand shot landed inside of two feet and he made the birdie putt after Van de Velde knocked in his par putt.
Els has not had an easy time this week. In the first round, he beat 64th seed Greg Kraft 3 & 2 and posted a 1-up victory on Thursday in beating Hidemichi Tanaka.
'The guys are playing at a high level right now,' said Els, who finished second in three majors in 2000. 'The guys aren't going to hang back. They're out there to win.'
Els will face Stadler on Saturday. Stadler came back to force extra holes after being 3-down with six holes to play. Stadler squared the match at the 16th after holing a 10-foot birdie putt.
The players halved the final two holes before going to number-one for the playoff. Coltart hit his second shot from 156 yards, landing the ball seven feet from the stick. Stadler was better. His second shot landed inside of two feet. Coltart pushed his putt right and then conceded the match to Stadler.
'I wasn't planning to be in this spot right now,' stated Stadler, referring to his deficit with six holes to play.
Stricker was dominant from the beginning in his match against Leonard, going nine-under through the first 12 holes.
'I was trying to put as much pressure on him as I could,' Stricker said. 'He's hit so many heroic shots at the Ryder Cup. At one point, I didn't want him to win a hole.'
Over 46 holes in three matches, Stricker has never trailed.
Stricker will meet O'Hern on Saturday. O'Hern, who is in this event because Jarmo Sandelin was a late withdrawal, has defeated three Americans on his way to the quarterfinals. O'Hern beat Sutton in 21 holes and defeated Tim Herron 5 & 3 on Thursday.
O'Hern spoke of his fourth-round match against his fourth American.
'If I can get ahead, we'll see what happens,' said the left- handed O'Hern. 'It's match-play so anything can happen.'
Faxon, winner of the 1993 Australian Open on this course, needed 18 holes to defeat the fourth-seeded Lehman. At number-16, Lehman left it in the bunker for his second shot. The miscue allowed Faxon two putts from 20 feet to take the advantage. He needed only one.
On the 17th green, Lehman had an opportunity to square the match, as his approach at the par-four hole landed five feet from the cup. Lehman was not able to capitalize, missing the putt.
Lehman needed to roll home a 25-footer for birdie at the closing hole to force a playoff but narrowly missed the putt right.
The Fulke/Campbell match came down to the final hole also. Campbell, ranked fifth in this tournament, made a five-footer to square the match at 17.
Both players hit the green in regulation at the par-four closing hole. Fulke had 25 feet and snaked a right-to-left putt into the cup. Campbell missed his birdie slightly left, giving the Swede a 1-up victory.
Taniguchi, fresh off a defeat of third-seeded Vijay Singh on Thursday, forced Appleby to concede on the 17th green. Despite hitting the lip of a fairway bunker at 16, Appleby halved the hole but was 2- down with only two holes to play.
At 17, Appleby drove left into the trees. His second shot landed in the rough with a tree obstructing his shot at the stick. Appleby hooked his third shot into a bunker and with Taniguchi on in two, the Australian conceded the match.
Maruyama, who came back on Thursday to beat Bob May, had little trouble in his match against McNulty. McNulty won the fourth hole but Maruyama squared the match at the next hole and never looked back.
In a tournament that featured only four of the world's top-10, only one has made it into the quarterfinals. Of the eight remaining golfers, three are seeded in the bottom-10.
The quarterfinals will be played Saturday morning and the winners will advance to the semifinals later that afternoon.