Sorenstam shares seventh place with Brittany Lincicome and five others.
Blomqvist had five birdies and one bogey on the Barseback course, where Sorenstam helped Europe win the 2003 Solheim Cup over the United States.
Hundreds of fans lined the course early to see Sorenstam hit her first ball of the tournament straight down the middle of the fairway. Sorenstam, the three-time defending champion, described her round as a 'rollercoaster.'
'I had a bunch of birdies and a bunch of bogeys,' she said. 'I'm not quite as pleased with my game as I could be. I missed several fairways and greens, but I hit some really good shots and putted well.'
The 36-year-old Swede, who had four birdies and three bogeys, also won the tournament when it was last played at Barseback in 2005.
'It's great to be back. Barseback is a fantastic place,' Sorenstam said.
Laura Diaz (69) and Louise Stahle (69) are tied for second at 3 under.
Maria Hjorth, who shared second at the Women's British Open at St. Andrews last week, was another stroke back at 70, along with Caroline Hedwall and Jade Schaeffer.
Schaeffer, who is playing her first full season on the Ladies' European Tour, chipped in from about 100 yards for an eagle on the par-4 17th hole.
'It pitched just 5 meters short and she went straight in the hole,' she said. 'It's the second approach shot I've holed this season.'