Rose surrendered a double-bogey on the 17th and then lost another shot on the last to drop to 10 under.
That put him at 11-under 133, three shots clear of Reed (72), Tommy Fleetwood (68) and defending champion Justin Rose (67).
Rory McIlroy finished 24 shots behind victor Xander Schauffele at the WGC-HSBC Champions in Shanghai.
Masters champion Patrick Reed said on Friday he was focused on winning the European Tour's season-long points race rather than making a point to his fellow Americans with his play at the WGC-HSBC Champions tournament in Shanghai.
Reed, playing an hour ahead of the final group, drove onto the front of the 16th green for a two-putt birdie.
The big-hitting 29-year-old from Utah picked up a shots on the par four 16th and then nearly made a hole-in-one on the 17th. "It was possibly an eight-under round with the chances that I had", said the world number three. He posted a number and made birdie on a playoff hole when it counted.
Tenth-ranked Jason Day of Australia totaled 71 and is tied for 24th, top-ranked Brooks Koepka and fifth-ranked Rory McIlroy of Northern Ireland are in a tie for 27th at 72, eighth-ranked Jon Rahm of Spain is tied for 41st at 73, second-ranked Dustin Johnson shot 74 and is tied for 49th, while sixth-ranked Francesco Molinari of Italy struggled to a 76 and is tied for 68th.
But the tables were turned on Saturday as the Englishman surrendered the crucial 54-hole advantage with a costly double-bogey on the par-3 17th after his tee shot leaked into a hazard. It's hard to swallow when you feel like you hit a good shot and you have a bad break like that.
"I was hitting the ball really solid", Reed said. Check in for highlights from every tournament plus player interviews, player profiles, tournament previews, swing analysis and all the greatest shots and unbelievable moments.
Reed has not crossed paths with Jordan Spieth since accusing his team mate of splitting up their partnership at last month's Ryder Cup.
"Tony is great, and he's due a win, to be fair", Fleetwood said.
The 29-year-old American took only four putts over the last four holes, starting with a tough up-and-down from a bunker behind the 15th green that barely reached the fringe and trickled down to about 4 feet. I felt like that was key because when it's windy like that, you have to have full control over it.