Sorenstam, the defending champion, hasn't played competitively since the Women's World Cup of Golf in January. She skipped the first two LPGA events of the season, but showed little rust in a bogey-free round that saw her tied for the lead at 5-under-par 67 with Silvia Cavalleri.
The score was three shots better than Sorenstam's opening-round 70 last year, when she came from behind during the final round to claim the first of her 10 titles in 2005.
But the 67 was nothing new: Sorenstam has opened three of her last four seasons with that score.
'I felt really good about my game, but you never know until you come out here and start putting your score together,' said Sorenstam, who has not finished outside the top-three in her last five season openers.
'You know what? I could not have asked for a better day,' she added.
Sorenstam's birdie on the first hole came after she pitched within 3 feet on her second shot. She added a birdie at the par-5 sixth, where she landed a sand wedge within 3 feet again.
'I am happy,' she said. 'It was the start I wanted.'
Things got better on the back nine, where Sorenstam carded birdies at 10 and 12 to get to minus-4. She added her fifth birdie at the par-5 18th, where she set up a 7-foot birdie putt with her sand wedge.
Four of her five birdies on the day were set up by the sand wedge.
'I hit a lot of fairways and a lot of greens and put myself in good position to make birdies out there,' Sorenstam said.
Cavalleri, who has never won on the LPGA Tour, carded seven birdies and two bogeys on Friday. She started on the 10th tee and played a bogey-free back nine, but stumbled to fives on two par-4s on the front nine.
'Apart from two bogeys on my back nine, it was just a really good round,' said Cavalleri.
Sorenstam and Cavalleri are trailed by Suzann Pettersen, who shot a 4-under 68 for sole possession of third place. Lorie Kane, Carin Koch and Mi Hyun Kim are one stroke further back in a tie for seventh.
For the first time in LPGA history, players were allowed to use carts. It helped them deal with the high altitude of BosqueReal Country Club.
'I prefer walking, but then again this course is very tough to walk,' said Sorenstam. 'I think using carts was the right thing to do. I think it will speed up play.'