Stenson's fellow Swede Patrik Sjoland is alone in second place at minus-12 after a 4-under 68. Simon Wakefield matched Stenson's 67 to take third place at 11-under-par 205, with Mikko Ilonen one stroke further back at minus-10 after a round of 7-under 65.
Early in the round, it was anyone's tournament as there were six players tied for the lead at minus-9. Stenson broke through that logjam with an eagle at the par-5 fourth. He followed that up with a birdie at the fifth to move to 11 under.
Stenson, however, stumbled to a double bogey at the sixth to create a seven-way tie for the lead. The Swede got one of those strokes back with a birdie on the ninth hole of the Duke's Course at Woburn Golf and Country Club.
The 28-year-old Stenson joined Sjoland atop the leaderboard when he birdied the par-4 14th. Stenson forged ahead with a birdie at the next. The 2001 Benson and Hedges International Open winner two-putted for birdie from 12 feet at the last to close at minus-13.
'I will just try and keep to my plan tomorrow and hopefully execute shots and play my way around the golf course like I did for the first three days and hopefully it will be enough,' Stenson said.
Stenson's game took a nose dive after winning three times on the European Challenge Tour in 2000 and once on the regular tour in 2001.
'I was struggling really bad in 2001 and the whole of 2002 really,' said Stenson. 'I had swing problems and after a while you get mental problems. My confidence was really gone for a long time. I managed to get it back at the end of last year and I have been playing probably the steadiest I have played on the four years I have been out here.'
Sjoland opened with a birdie at the first. He gave that stroke back when he bogeyed the par-4 sixth but was able to respond with a birdie at the seventh.
He made it two in a row when he birdied No. 8 and closed out the front side with another birdie at nine. Sjoland looked to be in control with a one-stroke lead.
However, Sjoland was unable to convert several birdies tries on the back nine. He parred the first eight holes of the back side, before two-putting for birdie at the par-5 closing hole to stay within one shot of his countryman.
'Playing with Henrik was good, we both played nicely and it will be fun again tomorrow, the only difference will be that it is in the final group,' said Sjoland of playing with Stenson in both the third and final rounds. 'I know if I can keep the ball in play and not make any stupid mistakes, then I can shoot 3 or 4 under every day and hopefully I can keep that going tomorrow.'
Graeme McDowell and Phillip Price, who shared the second-round lead, could only manage rounds of even-par 72. They share fifth place at 9-under-par 207 with Alastair Forsyth (66) and Mark Foster, who posted his third straight round of 3-under 69.
Carlos Rodiles and Welshman Ian Woosnam are one stroke further back at minus-8.