South African Louis Oosthuizen stormed into a three-stroke halfway lead at the Qatar Masters - and then pinpointed a new calm demeanour as the secret to his recent success.

The 26-year-old made a bogey-free seven-under-par 65 to top the second-round leaderboard on 12 under after dislodging former champion Andrew Coltart, whose solid 69 left the Scot a shot clear of Spanish youngster Alvaro Quiros (67) and Australia's Brett Rumford (69).

Oosthuizen, a five-time winner on his native Sunshine Tour, narrowly missed out on a maiden European Tour title last week in nearby Abu Dhabi. He finished runner-up there, after beginning his year with a 10th-place finish at the Joburg Open.

But after battling wet afternoon conditions at Doha Golf Club, which eased later in the day to allow Oosthuizen to pick up four shots in five holes around the turn, four years spent with coach Pete Cowan could pay off after he left 30 of the world's top 80 in his wake.

Oosthuizen, 82nd in the world, said: "I'm used to being very aggressive on the course, taking on every shot.

"I now try to stick with it, knowing I can make 20-footers for birdies so I just get myself into position on the green.

"I had a very big temper about two or three years back because I was frustrated that I was not playing better, but now I handle myself much more and I'm definitely having more fun.

"I've been working with Pete Cowan, my coach, and we are going forward and forward with my swing.

"With Pete I struggled putting-wise a few years back and I worked a lot on that and got much better and became much more consistent, so I don't need to be too aggressive.

"I can still make a score from just hitting the greens. Pete has helped me a lot, and my caddie Zach as well. The three of us are a great team and going forward."

Coltart was content with his "scrappy" second round, which followed his opening six-under 66, and will again look to come from behind over the weekend as he did in 1998 when he claimed the inaugural Pearl trophy.

"I'm pleased. There is always a question whether you can follow up a low round and I think I managed it," said 38-year-old Coltart.

"I think if you go around that course and shoot under par you have done really well and off the back of the 66 I was really proud of it.

"It's the type of game you cannot play the same one day to a next, but I got the job done with a couple of nice chips, a couple of nice pitches and a couple of nice putts and three under I'm happy with and I'm looking forward to the weekend."

Miguel Angel Jimenez sits five adrift in fourth, with fellow overnight leader and 2006 champion Henrik Stenson in a group a six under, a shot clear of Ross McGowan who leapt up the leaderboard with a bogey-free 66.

Sergio Garcia, Robert Karlsson and Lee Westwood are all at four under, with defending champion Adam Scott well down the field a further three shots back.

American Ryder Cup player Boo Weekley, his compatriot Brandt Snedeker, Abu Dhabi winner Paul Casey, Justin Rose and Colin Montgomerie all missed the cut.

Earlier Montgomerie refused to comment on Jose Maria Olazabal's decision to put himself forward for the 2010 Ryder Cup captaincy and jetted off to Dubai where the decision is expected to be made on Wednesday, before the Desert Classic begins a day later.

"I'm not saying anything significant today to anyone," he said.

"I will see you next week and I look forward to it."

Collated second round scores & totals

(Gbr & Irl unless stated, par: 72)

132 Louis Oosthuizen (Rsa) 67 65

135 Andrew Coltart 66 69

136 Brett Rumford (Aus) 67 69, Alvaro Quiros (Spa) 69 67

137 Miguel Angel Jimenez (Spa) 66 71

138 Rodney Pampling (Aus) 70 68, Damien McGrane 69 69, Chapchai Nirat (Tha) 69 69, Maarten Lafeber (Ned) 68 70, Henrik Stenson (Swe) 66 72, Paul Broadhurst 68 70

139 Anders Hansen (Den) 67 72, Ross McGowan 73 66, Johan Edfors (Swe) 72 67, Andrew McLardy (Rsa) 70 69

140 Sergio Garcia (Spa) 70 70, Robert Dinwiddie 67 73, Nick Dougherty 68 72, Peter Hedblom (Swe) 69 71, Anthony Wall 70 70, Aaron Baddeley (Aus) 68 72, Robert Karlsson (Swe) 68 72, Richard Finch 73 67, Lee Westwood 67 73

141 Charl Schwartzel (Rsa) 69 72, Magnus A Carlsson (Swe) 70 71, Peter Hanson (Swe) 72 69, Stephen Gallacher 72 69, Niclas Fasth (Swe) 70 71, Ernie Els (Rsa) 70 71, Markus Brier (Aut) 70 71, Gonzalo Fdez-Castano (Spa) 69 72, Thomas Levet (Fra) 71 70, Jyoti Randhawa (Ind) 71 70, Bradley Dredge 74 67

142 Jeev Milkha Singh (Ind) 70 72, Francesco Molinari (Ita) 72 70, Hennie Otto (Rsa) 73 69, Ross Fisher 71 71, Mikko Ilonen (Fin) 71 71, Oliver Wilson 69 73, David Howell 71 71, Simon Dyson 72 70, Gary Murphy 71 71, Stephen Dodd 70 72, Retief Goosen (Rsa) 69 73

143 Mikael Lundberg (Swe) 72 71, Robert Jan Derksen (Ned) 71 72, Steve Webster 72 71, Adam Scott (Aus) 73 70, Jarmo Sandelin (Swe) 68 75, Soren Hansen (Den) 72 71, Scott Strange (Aus) 72 71, Joakim Haeggman (Swe) 73 70, Marcel Siem (Ger) 72 71, Martin Kaymer (Ger) 71 72, Alexander Noren (Swe) 72 71, Paul Lawrie 72 71, Thomas Bjorn (Den) 70 73, Jamie Donaldson 70 73

144 Alvaro Velasco (Spa) 76 68, Danny Willett 73 71, Mads Vibe-Hastrup (Den) 73 71, Graeme Storm 72 72, Pablo Larrazabal (Spa) 73 71, Raphael Jacquelin (Fra) 71 73, Rory McIlroy 76 68, Jean-Francois Lucquin (Fra) 71 73, Gregory Bourdy (Fra) 73 71

Missed cut:

145 David Lynn 70 75, Mark Brown (USA) 72 73, Jose Manuel Lara (Spa) 75 70, Seve Benson 70 75, Paul Casey 76 69, Rolf Muntz (Ned) 72 73, Alastair Forsyth 75 70, Phillip Archer 71 74, Richard Green (Aus) 73 72, Ignacio Garrido (Spa) 74 71, Mark Foster 73 72, Brandt Snedeker (USA) 72 73, Gregory Havret (Fra) 71 74

146 Christian Cevaer (Fra) 77 69, Michael Lorenzo-Vera (Fra) 72 74, James Kingston (Rsa) 74 72, Colin Montgomerie 71 75, Ricardo Gonzalez (Arg) 75 71, Darren Clarke 73 73, Oliver Fisher 71 75, Justin Rose 74 72, David Dixon 70 76, Prayad Marksaeng (Tha) 72 74

147 Anton Haig (Rsa) 71 76, Soren Kjeldsen (Den) 72 75, Per-Ulrik Johansson (Swe) 74 73, Pelle Edberg (Swe) 74 73, Scott Drummond 75 72, Peter Lawrie 72 75, Thongchai Jaidee (Tha) 76 71, Boo Weekley (USA) 74 73

148 Shiv Kapur (Ind) 72 76, Paul McGinley 76 72

149 Felipe Aguilar (Chi) 74 75, Lee Slattery 75 74, Shiv Shankar Prasad Chowrasia (Ind) 75 74, John Bickerton 73 76, Kenneth Ferrie 75 74

150 Daniel Vancsik (Arg) 74 76, Martin Erlandsson (Swe) 76 74, Rafael Echenique (Arg) 77 73, Simon Wakefield 78 72

151 Ariel Canete (Arg) 77 74, Simon Hurd 77 74

152 Gary Orr 78 74

153 Michael Jonzon (Swe) 76 77

154 Emanuele Canonica (Ita) 71 83

155 Miles Tunnicliff 78 77

160 Max Williams 81 79