Jonathan Lomas was a shot behind in third with seven players a stroke further back at 5-under, including Scotland's Alastair Forsyth, Sheffield's Malcolm Mackenzie and former Ryder Cup Swede Jarmo Sandelin.
Scotland's Colin Montgomerie had to settle for a 1-over 73 after missing from two feet for birdie on the 18th.
Poulter was on the verge of getting into his Ferrari, complete with personalized number plate, and heading home to Milton Keynes after being taken ill before Wednesday's pro-am.
But the 27-year-old former rookie of the year decided to battle through it and has no reason to regret his choice.
"It was maybe a blessing in disguise that I felt so lousy so I was not trying too hard and went out with no expectations," Poulter said. "To shoot 65 is a massive surprise. If I felt as bad today as I did when I walked off the course after the pro-am I would have pulled out.
"However, I did win in Morocco with tonsillitis as well (in 2001), but I want to get them out because I've had enough of this."
Poulter had missed the cut in five of his last six events as he works on changes to his swing under the guidance of coach David Leadbetter.
"I needed to try and change a few things in my game to be more consistent," Poulter said. "I've always missed a few greens even when I was playing great so if I can tighten up those bad shots then I'll have more chances and hopefully be winning more golf tournaments."