K J Choi, a regular on the US Tour and whose only previous victory in Europe was the 2003 German Masters, is one shot ahead of Johnson and two better off than British Open winner South African Louis Oosthuizen.
The 40-year-old Korean carded a second round 67 in Stockholm to add to his opening 68 for a nine under par total while Oosthuizen added a two under par 70 to his opening 67.
Two weeks ago Choi switched to a “side-saddle” putting method, but after missed cuts at the John Deere Classic and then in the Open at St Andrews, he has gone back to a conventional style.
“I need more practice at it,” said Choi who eagled the long 15th – his sixth hole of the day – and birdied three of the next four.
Oosthuizen, bidding to be the first player to win a European Tour title the week following a British Open triumph, said he has no plans for any drastic changes to his putting style.
“You’ve got to do what you’ve got to do, but I think I’ll stick to my routine,” said the 27-year-old South African.
Johnson’s only European Tour success was eight years ago in Australia, but the 33-year-old’s bogey-free 66 was the low round of the day.
Johnson’s compatriot and playing partner Jesper Parnevik, out of golf since February after the discovery of a career-threatening fractured vertebrae, quit after 11 holes of his second round.
That was longer than he feared he might last and Parnevik, five over at the time, will now continue the rehab which he hopes can make him a Tour regular again.
Italian Edoardo Molinari, who with a second place finish could knock Luke Donald out of the all-important top nine on The Ryder Cup table, is at five under.