Both mainstays of the LPGA Tour, Rosales and Delasin anchored their strong first-round card on a swashbuckling front-nine stint where they canned in four birdies before finishing five-under in the day, tied with Australia, Japan and Sweden.
The format of play for the opening round was betterball with each member of the two-person teams playing their own ball and the best score counting at each hole on the tortuous par-73 links-style course which hosted the 2003 Presidents Cup.
Going four-under after the front nine, Rosales and Delasin gained another stroke with birdies on Nos. 13 and 16 against a bogey on No. 12.
Lori Kane and Dawn Coe-Jones from Canada, who were 25-1 outsiders at the start of the week, posted the early lead, with Kane doing most of the damage as she racked up seven birdies of her own. But Coe-Jones helped out at crucial moments to keep the score going.
However, the 66-1 rank outsiders from Italy, Diana Luna and Giulia Sergas, fought back after a double bogey seven at the ninth hole and rattled off six birdies on their back nine for a 31 and tie for the lead in this $1million event.
A shot behind Japan, Australia, Sweden and the Philippines are England, Mexico and the USA.
And Wales, despite reaching five under par through 14 holes, squandered a couple of shots to drop back to three under par to take sole possession of 10th place in this 20-team field.
"We hammed and egged it very well," said Kane a four-time winner on the LPGA Tour before her partner interjected.
"I mean she made nine, ten," said Coe-Jones. "I don’t know how many she made. I helped her twice! When she needed a par, I was there."
"Yes, and big ones," replied Kane. "It’s more about momentum at the time and we kept the momentum going instead of falling back. On the tenth hole, I am on the green in two and didn’t putt very well. Dawn is in the fairway bunker and makes a hell of a four, and we needed that to keep us rolling. Then I followed up and birdied the next one. That is what it was about today."
Sergas, who professes a love to skydiving, admitted that the pair had a huge adrenaline rush when they closed out their round with five straight birdies around this Gary Player-designed layout.
"It was the team, the team, the team because we had maybe the same number of birdies. It was both. It was really good teamwork."
Luna agreed that the double bogey on the ninth holes spurred them on and when the adrenaline kicked in, they were rolling putts in from everywhere.
"I think in a way, maybe that (double bogey) gave us the courage to play the second nine like we did. Maybe we needed that," said the Tenerife Ladies Open champion of 2004."