The 27-year-old Sanchez, who famously beat Min Woo Lee to win the 2017 Australian Amateur crown, carded a bogey-free round of seven-under 64 on the Remarkables course - one of two layouts in use this week at Millbrook Resort.
The Victorian finished his round at 8.16pm local time.
New Zealand amateur Yuki Miya was in outright second at six under through 13 holes when play was called off for the day.
Sanchez won his maiden event on the Australasian Tour last year when he saluted in the Webex Players Series South Australia.
"I was just really happy to get it done today, get the round in," he said after a long day where the start of play was pushed back three hours because of heavy overnight rain.
"It rained a bit early and there was a bit of wind around and then that drifted away and it was pleasant towards the end.
"When I woke up this morning and it was raining pretty heavily and we got the notification of the suspension of play, you've just got to adjust to whatever they tell you."
Fellow Australian Wade Ormsby carded one of the rounds of the day in the worst of the conditions, a five-under 66 on the more difficult Coronet course, to be tied for third with American Kevin Na and Kiwi star Daniel Hillier, who will have to complete the final five holes of his opening round on Friday morning.
South Australian Ormsby has plied his trade on a number of tours throughout his career and was a late call-up to LIV Golf Adelaide earlier this month, replacing the injured Phil Mickelson.
But he is still chasing a maiden win on the Australasian Tour and would dearly love to tick that ambition off this week.
"It was pretty tough out there early - cold and wet and windy," said Ormsby.
"I was just trying to put it in damage control at the start and I played some pretty good golf towards the end there so I'm happy."
Playing his first tournament since becoming the first LIV Golf team captain to be dropped, Na signed for a bogey-free 66.
The American was even able to make light of a slice of bad luck on his 10th hole, when his second shot cannoned into his amateur partner's ball, costing him at least 70 metres.
"When I saw the weather forecast I was like 'oh no, I've got the bad draw'," said Na, who has won five times on the PGA Tour.
"It wasn't easy, there was a three-club wind with the rain at times."
Rising Kiwi star Kazuma Kobori was in a group tied for sixth at four under after a round of 67 highlighted by a hole in one.
The DP World Tour player holed out with a 4-iron on the 210m 4th hole on the Remarkables course, only three months after he achieved the same feat on the party hole at the Australian PGA.
"It's actually playing pretty tricky here," said Kobori.
"I thought someone was going to go ballistic out there but no one has so far. So four under is pretty good.
"I made a few sloppy mistakes but we can tidy that up over the weekend."
Defending champion Ryan Peake and LIV Golf star Lucas Herbert were both at one over through 13 holes when the hooter sounded to end play for the day.
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