Johan Edfors, a two-time winner this season on the European Tour, shot a 2-under 69 on Friday. He is tied for second place with Charl Schwartzel (66) and Damien McGrane (66) at 8-under-par 134.
David Drysdale, who shared the first-round lead with Edfors, posted a 1-under 70 in round two. He is tied for fifth place with Jamie Donaldson, who shot a 4-under 67, at minus-7.
Clarke collected his first birdie of the second round at the par-5 third, a hole he has birdied in each of the first two rounds. He added birdies at six and nine to make the turn at 3-under-par 33.
He stood at 8 under par for the championship and pushed it to minus-9 with a birdie at No. 10. Clarke dropped his only stroke of the round at the par-3 11th, but the 38-year-old more than atoned for his miscue there.
Clarke got back into sole possession of the lead at 9 under par with a birdie at the 14th. He moved to 10 under when he ran home a 12-foot birdie putt at 15, but saved his best shot for later in the round.
He missed a 35-footer for birdie at 16, but stepped onto the 205-yard, par-3 17th tee with a 6-iron. Clarke's ball stopped a foot from the cup and the Ulsterman tapped in for a birdie to get to minus-11.
At the par-4 18th, Clarke hammered his drive down the fairway and only had a 9-iron in his hand for his second shot. Clarke pushed his approach right of the putting surface, but hit his third to tap-in range.
Clarke converted the par putt and will take the 36-hole lead on the European Tour for the first time since the 2003 Dunhill Links Championship, when he went on to tie for fourth place.
'I hit it really nicely today and gave myself an awful lot of chances,' said Clarke. 'I missed a few, unfortunately, but overall 6 under is pretty good. I have been working on a few things with Ewen Murray and trying to hit the ball as hard as I can. If the club is in the right position then I can do that and I am feeling quite comfortable with what I am doing.'
Clarke has not won on tour since the 2003 World Golf Championships - NEC Invitational, but his excuse for not visiting the winner's circle is bigger than golf.
Clarke's wife Heather has been battling cancer over the past few years, so Darren has taken time away. He stated earlier in the month that the Ryder Cup, which will be played in two months, has not entered his mind as his focus is at home.
If Clarke were to hold on and hoist the trophy on Sunday, many, if not all, European Tour members would be happy.
'Darren played very well and if he plays anything like that over the weekend then he should be okay,' said Colin Montgomerie, who played with Clarke over the first two rounds. 'I'd be delighted to see him win. His troubles are well- broadcast and I wish him well. Now, he's three ahead and we all wish him well.'
Defending champion Tim Clark is in position to repeat after a 4-under 67 on Friday. He is tied for seventh place with Thomas Bjorn (64), Gregory Havret (67), Andres Romero (64), Raymond Russell (69) and Lee Westwood (67). The group came in at minus-6.
Luke Donald (69) and Ian Poulter (67) headline a group tied for 13th at 5-under-par 137. Montgomerie (66) and Sergio Garcia (67) are part of a group in 17th at minus-4.
Ernie Els and Retief Goosen both carded rounds of 2-under 69 on Friday and are in a logjam tied for 29th at 3-under-par 139.
The 36-hole cut fell at 1-under-par 141 with 69 players making it to the weekend.