Defending champion Luke Donald is one stroke further back after an opening round of 5-under-par 66. He was joined there by Peter Hedblom and world No. 6 Sergio Garcia.
Sandelin got his round going with a birdie on the first. He gave that stroke back with a bogey on the par-4 fourth. After a pair of pars, Sandelin caught fire.
The 38-year-old birdied the seventh, then Sandelin moved to 2-under as he birdied the par-5 ninth. Around the turn, he made it two in a row as his birdie try on the 10th found the bottom of the cup.
Sandelin got it to 4-under as he birdied the par-4 12th at Crans-sur-Sierre. The five-time winner on the European Tour then birdied the 14th and 15th, both par-5s, to end at minus-6.
'Today I missed a lot of fairways, but I managed to hit a lot of greens and the putting feels good,' Sandelin said. 'This was very satisfying. I have been struggling for three or four years. It's been a tough stretch, especially this year, which is my worst, but I am always very positive and confident in my mind that the wind would change and this is my best first round in four years.'
Houston started on the back nine and opened with a bogey on the 10th. He got that stroke back with a birdie at 15. Houston moved into red figures with a birdie at the 17th.
Around the turn, the Welshman eagled the par-5 first to move to 3-under. Houston stumbled to another bogey on the fourth. He erased that mistake with a birdie on No. 5. After an eagle on the short par-4 seventh, Houston birdied the eighth to share the lead.
'It started badly with a clumsy bogey, then I settled down and got out in 1-under and the eagle at the first kick-started everything,' said Houston. 'The second eagle was lovely at the seventh -- a solid driver to six feet and the two at the next was good too.'
Carter also started his round on the second nine and picked up his first birdie on the 11th. He took advantage of the par-5 15th as he birdied that hole and made the turn at minus-3 thanks to a birdie on the 18th.
The Englishman made it two straight as he birdied the first. Carter parred five holes in a row before carding his fifth birdie of his round on the seventh. He came right back to birdie the eighth before a par at the last closed out a bogey-free round.
'I played very sensibly and when I missed the green, I missed on the right side,' Carter said. 'I chipped and putted well, never in much trouble and basically did most things well.'
Paul Casey carded a 4-under-par 67. He was joined in a tie for seventh place by Leif Westerberg, Oliver Wilson, Michael Jonzon, Richard Bland, Paul Broadhurst, Christian Cevaer and Anders Hansen.
This event is serving as the first tournament for European players to earn points as they attempt to qualify for the 2006 European Ryder Cup team