Els will face Thomas Bjorn, his neighbor in the area, in the final on Sunday after the Dane disposed of British Open champion Ben Curtis, 2-up.
'It's great to play in the final again,' said Els. 'I think it's my sixth final now, and I'm looking forward to it.'
Els, who will try to join Gary Player and Seve Ballesteros as the only five-time winners of this event, looked to be in trouble during the morning session at Wentworth and found himself 4-down after a bogey at the 13th.
Singh bogeyed the very next hole but Els relinquished that win with a bogey of his own at the 15th.
'Vijay was totally dominating me this morning,' said Els. 'I was really, really not playing good. I wasn't feeling comfortable this morning.'
Despite the struggles, Els shifted the momentum in the match with a win at the par-4 16th after his approach from a bunker stopped within two feet of the cup for a birdie.
Els then won the 17th and the 18th with birdies to go 1-down after the first 18.
Singh squared the match with a bogey at the first hole in the afternoon and Els took his first lead of the day with a birdie at the second. Singh then lost the third with a bogey and Els took a 3-up lead with a birdie at the fourth.
The 40-year-old fell 4-down with a bogey at the fifth and 5-down with a bogey at the seventh.
'Vijay gave me a nice, gentle start to the second round,' said Els, who won his eighth consecutive hole when Singh bogeyed the fifth. 'I was just trying to play and stay focused and hit the next shot. I don't know what he had for lunch, but he just didn't quite hit the ball the same.'
Singh responded with a win at the eighth after his second shot stopped six feet from the cup. Singh looked to continue his comeback at the par-3 10th but he missed the green off the tee.
While Els found the putting surface, Singh persisted and chipped in for a spectacular birdie. Moments later, Els, who had upwards of 40 feet to the hole, ran home the putt for the halve.
'Luckily I made that putt on 10,' said Els. 'That was a long putt and I just gave it a whack and it went in.'
Singh picked up another birdie at the 11th to win the hole and get to 3-down and he looked to capture another at the following hole. At the par-5 12th, Singh, with the sun in his eyes, hit his second shot within four feet of the cup.
Els did him one better.
The defending champion landed his approach inside Singh's, and both players converted their eagle putts to halve the hole.
'I started to come back but Ernie was also playing well and he didn't make too many mistakes,' said Singh.
Els increased his lead to 4-up with a birdie at the 13th and converted a six-foot putt for a par at the 14th to put the pressure on Singh.
Singh, who defeated Els in the final to win this event in 1997, had the same distance for a par of his own but he failed to convert, handing the match to Els.
The other semifinal match was much closer as Bjorn carried a 1-up lead heading to the par-5 18th.
Curtis, who won his first major title at the hands of Bjorn's late collapse at Royal St. George's this summer, never led on Saturday but Bjorn could not shake the American.
'Ben is a good player,' said Bjorn. 'He's got a great career ahead of him.'
Curtis hit his second shot to 12 feet at the 16th and Bjorn conceded the hole after an errant drive nestled against a fence.
Both players parred the 17th but Curtis could not keep up with Bjorn at the par-5 last.
Bjorn reached the green in two while Curtis played his second shot over the putting surface. Rather than trying to chip in and test Bjorn's putter, Curtis conceded the match allowing Bjorn to advance for a final showdown with Els on Sunday.
'Tomorrow will be a strange day for us in the sense that we are good friends and we see each other a lot outside the golf course,' said Bjorn. 'But I think we are going to put that aside and go out and do the best we can.'