South African Hennie Otto fired a 3-under 69 to move into second place at 5-under-par 211. Spaniard Jose Manuel Lara tied for the low round of the day with his 4-under 68. He shares third place at 3-under-par 213 with Scotsman Paul Lawrie (69).
Hanson got off to a hot start with a birdie at the first. He then drained a 25-foot birdie try at the third to move to minus-8. The Swede tripped to his first bogey at the par-4 fourth.
The 27-year-old, who is looking for his first European Tour win, drained a birdie try at the sixth before dropping in a 10-foot birdie putt at the seventh on the Old Course at San Roque Club.
Hanson slipped to another bogey at the par-4 eighth. He two-putted for birdie on the par-5 ninth to move to 9 under and four strokes clear of the field.
Hanson stumbled to a three-putt bogey at the 10th, but his lead was still four. After two-putting for par on four straight holes, Hanson was unable to get up and down for par from short of the green at 15 to drop back to 7 under. He parred his final three holes to remain two shots clear of Otto.
'I got off to a great start with two early birdies, but then the back nine was very difficult,' said Hanson, whose best finish on the European Tour came at last year's Scandinavian Masters when he finished second. 'Four three-putts wasn't great and made the difference between a very good lead and two shots, but overall I'm very pleased.
'I was aware that I had a big lead, but there was a long way to go and still is. There is still a round to go. I am happy I am in the position I am. Hopefully I can win tomorrow.'
Otto, who is also looking for his first European Tour win, tripped to a bogey at the first, but came right back with a birdie at the next. He converted consecutive birdie tries from the fifth to move to 4 under.
The South African birdied the ninth, but tripped to a bogey on No. 10. Otto slid back to minus-3 after a bogey on the 14th. He erased that mistake with a birdie on 15 and moved into second place with a birdie on the 17th.
Lara, one of two Spaniards in the top 10, carded six birdies and two bogeys in his round of 68. That helped him jump into a share of third place from a tie for 22nd.
'It was a little easier out there today, a little less wind and blowing from the opposite direction, but still a tough day,' said Lara. 'It is one of the toughest courses tee to green we will face all year. I have given myself a chance. Tomorrow I need to do it again and see what happens.'
Peter Gustafsson and Robert Karlsson, a pair of Swedes, share fifth place at 2-under-par 214. They are joined there by Ireland's Peter Lawrie.
Miguel Angel Martin, Gregory Bourdy and Sebastian Fernandez are tied at minus- 1 and are the last of just 10 players in red figures.