Day to face Dubuisson for WGC Match Play crown
Victor Dubuisson of France reacts during the World Golf Championships - Accenture Match Play Championship at The Golf Club at Dove Mountain on February 23, 2014 in Marana, Arizona - by Andy Lyons
Dubuisson, ranked 30th in the world, sealed the victory on the 18th green with a superb lag putt from 35 feet to set up a par that was good enough for the win after Els was unable to get up and down from a greenside bunker.
The 23-year-old Frenchman had battled back from 3 down through four holes, and kept his nerve through a tense back nine that saw Els square the match with a 30-foot birdie putt at the 16th.
In Sunday afternoon's 18-hole championship final, Dubuisson will take on last year's third-place finisher in Day, who defeated American Rickie Fowler 3 and 2.
Dubuisson, who won his first European Tour title at the Turkish Open in November, looked shaky early against Els, but he steadied himself with a strong par save to halve the seventh, then won eight and nine with back-to-back birdies.
Dubuisson squared the match with a tap-in birdie at the par-five 11th after Els missed a seven-footer.
Dubuisson grabbed his first lead of the day at the par-three 12th, where Els missed the green and couldn't get up and down.
The South African Veteran squared the match at 14th, where Dubuisson needed four strokes to reach the green.
Dubuisson responded with a birdie to win the 15th, only for Els to even the match again.
Day never trailed in his match against Fowler after winning the first hole with a birdie.
Day went 3 up with birdies at seven and eight before Fowler pulled a hole back when Day's approach at the ninth landed in a rocky patch of cactus.
The Australian's first attempt to get out hit a cactus and bounced back toward him in another awkward lie.
After his attempt at a left-handed fourth shot Day conceded the hole, but he stretched his lead back to 3 up with a birdie at the par-five 11th.
Fowler won the next two to trim the deficit, Day missing a six-footer for par at the par-three 12th and three-putting for par to lose the par-five 13th, where Fowler drained a seven-footer for birdie.
Fowler couldn't get any closer however, and after Day won the 15th the match ended with Day's par at 16, where Fowler three-putted from six feet.