Overnight leader Brian Davis stumbled to a 1-over 73. He was joined in a tie for second place at 3-under-par 213 by David Howell (72) and Steve Webster (70). Thomas Bjorn stands alone in fifth place at minus-2 after a 1-over 73 on Saturday.
Campbell had a steady front nine in the breezy, cool conditions on the Arden Course at the Marriott Forest of Arden Hotel & Country Club. He rolled in a birdie try on the par-four second.
The New Zealander came back with a birdie on the ninth to move to minus-3. Campbell tripped to a bogey on the 10th, but got that stroke back with his third birdie in three days on the par-5 12th.
Campbell faltered to another bogey at the 14th to drop back to minus-2. The 36-year-old ran home a 35-foot birdie putt on the 15th to begin a solid stretch of golf.
The six-time winner on the European Tour made it two in a row with an 18-foot birdie putt on the par-4 16th to get to 4 under and a share of the lead.
Campbell was not done. He two-putted for birdie on the par-5 17th to get to 5 under. Campbell capped a run of four straight birdies as he chipped in from over the green at the last to finish off a round of 67.
'I consider myself a pretty good front runner,' said Campbell, whose last win came at the 2003 Irish Open. 'I think the boys chasing me know that as well.'
Davis opened with five straight pars before converting back-to-back birdie putts from the sixth to climb to 6 under and a one-shot lead. However, around the turn the Englishman struggled to three straight bogeys from the 10th to fall out of the lead.
The 30-year-old got one stroke back with a birdie on the par-4 14th. Davis tripped to another bogey on the par-5 17th before a par at the last.
Howell got off to a hot start with birdies at two and three to grab the early lead. He fell out of the top spot with a bogey on No. 5. The Englishman moved back to 5 under with a birdie on the par-5 seventh.
The 29-year-old struggled mightily on the back nine. He bogeyed the 10th, 13th and 14th to tumble back to minus-2. Howell recovered one stroke with a birdie on 17 to share second place.
'I just got on a bad run and lost some momentum,' said Howell. 'I had a couple of putts about six feet which could have changed the day, but missed them. I would rather be in Michael's position, but three shots around here is nothing on a course like this.'
Webster stumbled out of the gate with a bogey on the first that dropped him to even-par. He atoned for that error with birdies at two and four. However, Webster struggled to a double-bogey on the sixth to again drop to even-par.
The Englishman caught fire from there. He rolled in a birdie try on the seventh, his third in three days on that hole. Webster came back with a birdie on the ninth to make the turn at 2 under.
Webster moved to minus-4 thanks to birdies at the 11th and 12th. However, he tripped to a bogey on 16 to end at 3 under.
'I feel I am more focused on getting the job done than I was last year and that is why my results have been consistent this year,' Webster said. 'Hopefully I can continue that tomorrow.'
Gary Murphy fired a 4-under 68 to move into a tie for sixth place at even-par 216. He was joined there by Maarten Lafeber (70), Paul Broadhurst (70), Robert-Jan Derksen (70) and Oliver Wilson (71). Soren Hansen and Simon Khan are one stroke further back at plus-1.
Barry Lane, the defending champion, bogeyed three holes on the back nine en route to a 1-over 73. He stands in a tie for 16th at 3-over-par 219.