Stephen Gallacher bogeyed his final hole to drop out of a share of the lead. He was joined in second place by Ross McGowan and Louis Oosthuizen at minus-3.
Two-time defending champion Paul Broadhurst shares fifth place with Barry Lane and Nick Dougherty. That trio is tied at 2-under-par 69.
Prior to the opening round, officials decided not to cut the greens. This decision was made with high winds in the forecast. That was a wise decision because the wind gusted up to 30 mph causing many problems on the greens.
'We all had a few putts that could have made us look stupid and if the greens had been cut we might not have been able to play,' said Dyson. 'But it's understandable why they made that decision, if they had been cut I don't think that we could have finished the round. It was a matter of keeping your head.'
With the setup at Quinta da Marinha Oitavos Golfe this week, players teed off the first and eighth, instead of the normal first and 10th tees.
Dyson began his round on No. 8 and birdied the par-5 hole. He parred three straight from there before dropping in a birdie putt on the par-3 12th.
The 29-year-old Dyson drained a 20-foot eagle putt on the par-5 16th to jump to minus-four. He ran off six straight pars around the turn.
Dyson drove into the brush left of the fairway at the fifth, his 16th. He pitched his second out to the fairway, then left himself over 50 feet for par.
He was unable to sink the long par putt and walked off with his first bogey of the day. Dyson rebounded with a birdie on the par-5 seventh, his last. He putted from the fairway short of the green within 3 feet and kicked that in for a closing birdie.
Gallacher also started on the eighth and he opened with back-to-back bogeys. On the back nine, he made up those strokes and more. He collected four birdies, including three in a four-hole span, to get to minus-2.
The Scotsman tripped to another bogey on the first. Gallacher erased that mistake with a birdie on two. He then birdied four and six to gain a share of the lead. However, he bogeyed the par-5 seventh to end one back.
Oosthuizen had a solid front nine with seven pars and two birdies. He dropped in consecutive birdies from the 10th to move to minus-4. After a pair of pars, the South African stumbled to a bogey on the par-3 14th. He parred out to share second place.
McGowan started with a pair of pars from the eighth. Around the turn, he birdied the par-four 10th then eagled the short par-4 11th to move to 3-under.
The Englishman birdied the par-5 16th to move into the lead at minus-4. On the front nine, McGowan faltered to a bogey at the par-4 second. He parred his final five holes to finish at minus-3.
Gary Orr, the 2000 champion, opened with a 1-under-par 70. He shares eighth place with Gonzalo Fernandez-Castano, Raphael Jacquelin, Sven Struver, Tiago Cruz and Robert-Jan Derksen.