The Holywood star missed a string of putts inside 10 feet and then hit a couple of wild drives into the desert to find himself two down with five to play.
But displaying the kind of class that saw him become world No 2 two years ago, he sensationally birdied the 14th, 15th and 16th to go one up before English hit back with a birdie from 19 feet at the 17th to level the match and take it to the 18th.
But after halving that one in pars, it was McIlroy who threw it all away at the first extra hole, pulling his second in the desert from where he took two more to get on the green.
The two-time major winner could have been a couple up with eight holes to go but instead found himself all square after missing four putts inside 10 feet.
He should never have lost the par-five second after English bunkered his drive. But he walked off one down after pulling his approach with an iron into trouble.
He got back to all square straight away, hitting a sky-high tee shot to six feet at the 202 yard third.
But after being forced to chip and putt for a half at the fifth, he missed a six foot birdie chance to win the par-three sixth after another sensational iron shot.
English took the seventh in birdie after McIlroy missed a seven footer and while the Ulsterman got back to level again with a birdie at the par-five eighth, he missed two putts inside 10 feet at the ninth and 10th to find himself one down.
A wild push into the desert at the par-five 11th forced him to take a penalty drop and he ended up conceding the hole to go two down.
He hit back with a birdie from 10 feet at the par-three 12th but another wild tee shot sailed right into the desert at the par-five 13th and after taking two to get back into the semi-rough, he ended up two putting for bogey to go two down again.
The former world No 1 was in danger of an early exit for the second year in a row but he showed is class, hitting an eight iron to six feet and converting for birdie at the 14th.
At the driveable par-four 15th he elected a three wood and got up and down from right of the green to square the match after English had chipped weakly. Then at the 235-yard 16th, he hit a stunning mid-iron to four feet and rolled in the putt for his third two of the day and a one up lead.
Graeme McDowell was two down with four to play against the hugely talented Japanese star Hideki Matsuyama, 22 next week, having come back from three down after just six holes.
Matsuyama birdied the first, chipped in for eagle at the second and won the sixth with par-three to streak ahead before McDowell birdied the seventh and eighth to get back to one down at the turn.
But he bunkered his tee shot at the 14th and bogeyed to go two down as Matsuyma made a 12 footer for birdie.
Sergio Garcia came back from two down after seven holes to beat close friend Bill Haas 3 and 1, covering the next 10 holes in five under with an eagle three at the eighth — he was 70 yards wide in the desert on the right but recovered with a 200-yard seven iron to 10 feet — and winning birdies at the 12th, 14th and 17th.
“It was definitely important to win that hole mainly because I just came off missing a two and a half footer on six to win the hole,” Garcia said. “It was important to win that and not give him the chance of making the birdie putt and halve the hole, and kind of get a little bit more momentum on my side.”
Garcia will now play American Rickie Fowler, who came back from one down after 15 holes to beat the in-form Jimmy Walker one up.
French debutant Victor Dubuisson, currently inside the automatic qualifiers for the European Ryder Cup side, beat Peter Hanson 3 and 1 to set up a last 16 match with Bubba Watson, who beat Swede Jonas Blixt 2 up.
American Jordan Spieth showed just why he’s considered one of the hottest young players on the planet when he crushed Danish veteran Thomas Bjorn 5 and 4
No 1 seed Henrik Stenson lost 4 and 3 to South Africa’s Louis Oosthuizen who will face Webb Simpson, a 5 and 4 winner over Brandt Snedeker.
(USA unless stated):
Sergio Garcia (Spa) bt Bill Haas 3&1; Rickie Fowler bt Jimmy Walker 1 up; Victor Dubuisson (Fra) bt Peter Hanson (Swe) 3&1; Bubba Watson bt Jonas Blixt (Swe) 2 up; Jordan Spieth bt Thomas Bjorn (Den) 5&4