Campbell, who returned along with half the field to complete the darkness-suspended second round Saturday morning, tacked on a 65 to his opening 62 for an impressive total of 17-under-par 127. His closest pursuer is Eduardo Romero, who wrapped up a bogey-free round of 5-under 67 before noon for sole possession of second place at 11-under par.
Ireland's Paul McGinley, who tied for second last week at the International Open, matched Campbell for low second-round score with a flawless 65 that lifted him into third place at minus-10.
Campbell, the winner of the Heineken Classic in February, is seeking his fifth European Tour title after a breakthrough season in 2000 that saw him win three times.
Although the 32-year-old from Wellington suffered his first bogey of the tournament two holes before he played his last on Friday at the 11th, he came back in the morning with birdies at Nos. 14, 17 and 18 for a total of 18 birdies in 36 holes.
'I got off to a flyer with four birdies in the first five holes the day before and it was just a matter of preparing yourself again,' said Campbell, the 18th-ranked player in the world. 'I felt very good when I went to the 12th hole this morning. The key to my rounds is that I'm driving the ball so well, making the harder holes a lot easier.'
Campbell has hit 23 of 28 fairways and 30 of 36 greens through two rounds.
Argentina's Romero, nicknamed 'El Gato' (the cat), missed the early part of 2001 because of a serious dog bite on his leg that took over two months to heal. He posted his first top-10 of the season last week with a tie for seventh at The Belfry.
The 46-year-old Romero, who captured the 2000 European Masters in Switzerland, has been amazed by the performance of the leader.
'Michaels golf is unbelievable,' Romero said. 'I played with him last week and he missed the cut, but his playing partner, Miguel Angel Jimnez, told me last night he is playing perfect golf.'
Colin Montgomerie, another player to make his way around without a mistake over the second set of 18 holes, used his 6-under 66 to join England's John Bickerton at eight-under. Montgomerie's game looks to be peaking just in time for his title defense at next week's Volvo PGA Championship in England.
World No. 1 Tiger Woods carded two second-round eagles -- a chip-in at the fifth on Friday and a long putt at the par-5 16th Saturday morning -- for a 68 and a share of sixth place at 7-under 137 with seven others, including Ernie Els and defending champion Lee Westwood.
'Hopefully I can go out this afternoon and post a low number and see where we finish,' said Woods, who will seek his fifth straight major title at next month's U.S. Open. 'Ive played in spurts -- some good shots at times and some shots that arent that good.'
Woods triumphed at this event in 1999, the only other year it was held at St. Leon Rot.
The cut fell at 1-under-par 143 and included Northern Ireland's Darren Clarke, who upset Woods in the final of the 2000 WGC-Match Play Championship. Clarke, all but assured of missing the cut after a first-round 76 and two bogeys over the front nine of the second round, landed right on 143 after recording a back-nine 29 Saturday morning that featured five birdies and an eagle.
'I just wanted to get out of the way of Monty and Tiger. I cant explain where that finish came from,' Clarke said.
Full-field scores from the Deutsche Bank - SAP Open