McIlroy walked away hand-in-hand with tennis star girlfriend Caroline Wozniacki after a seven-birdie, bogey-free display that means he might yet complete a two-week Chinese double.
The 22 year old US Open Champion beat American Anthony Kim in a play-off for the Shanghai Masters last Sunday and the winner at Sheshan International will receive €842,217.
Westwood, twice a runner-up at the event, did not drop a stroke either and, with Ernie Els down in 53rd place in the 78-man field, could well take over as the greatest money-earner in European Tour history. He currently has €25,848,392 to the South African's €26,100,907.
It is Jacobson he is trying to catch rather than Els, though, and the three-time European Tour winner was delighted with his day's work.
He had a hat-trick of birdies from the second and bounced straight back from a bogey at the difficult ninth with one of his 15 footers at the next.
A 25 foot putt followed three holes later and the one on the next was a real bonus after he had driven into the rough and been forced to lay up.
In the early stages England's Paul Casey had loomed as potentially the biggest threat.
After a year of battling a foot injury, Casey was only two back after an 18 foot eagle putt at the eighth.
But after completing an outward 32 he was disturbed by a noise on the tenth tee, sent his iron into thick rough and double-bogeyed.
Chipping in at the 12th repaired some of the damage, but he closed with a bogey six after his approach to the par five landed on the bank and rolled back into the water.
A 70 left him ten under and in a tie for eighth spot, one stroke behind Graeme McDowell (67) and Martin Kaymer (68).
Last year's Open Champion Oosthuizen was inches away from doing the same thing as Casey on the 538 yard last, but the ball clung on to the fringe and he two-putted for birdie and his second bogey-free round in a row.
Round of the day was a 64 from China's 24 year old World Number 959 Zhang Xin-jun, and his presence alongside Casey and American Bo Van Pelt on ten under should swell the crowd no end on the final day.
Jacobson said: "I've still got to shoot a good score, but they will have to catch me. I sometimes feel a little bit stressed if I start off a few shots behind, so I prefer any time I can get a lead.
"I do feel good about my game and it's nice to make some long putts.
"It's a little bit of a bonus when you make the long ones, but that's sometimes what happens in a round.
"I try not really to worry about the result too much and focus on the procedure and the shots and the routine, and where to hit the ball. That normally takes care of a lot of potential tension."
McIlroy said of his 65: "It's definitely what I needed to give myself some sort of chance.
"I was five behind going into the last day at the Dunhill (at St Andrews last month) and made a good charge and hopefully I can do the same again.
"I just didn't make silly mistakes. I feel as if there's a lot of good scores in me and I was able to produce one of those today."
Westwood said: "I really didn't hit it very well. I struggled with my swing and wasn't very consistent.
"But I putted well and I'm going to have a chance to win the tournament. That's all you ever ask at any tournament."