The Englishman is tied with German Jeremy Paul and Norway's Kris Ventura at Vidanta Vallarta.
A group of five players - South Africa's Aldrich Potgieter, Argentina's Alejandro Tosti and American trio Isaia Salinda, Brian Campbell and Patrick Fishburn - are a shot off the pace.
Aaron Baddeley is the top-ranked Australian, tied 18th after a four-under 67.
Baddeley finished the opening round strongly, producing birdies on three of his final four holes.
Ventura was the only player to reach eight under, running off three straight birdies late in his round. But he missed the green on the par-three ninth, his final hole, chipped to 10 feet and missed the par putt.
"Bummer with the last hole, but other than that, really solid," Ventura said.
"Could have made some more birdies, obviously, but just happy where my game is. I can't expect to hit it like this every single day. Today was just one of those days where everything was spot on."
Former Open champion Francesco Molinari is among a large group of players on five-under-par despite opening with a double bogey six.
The Italian rallied with four birdies before the turn, adding an eagle at his 16th hole and a birdie at the last.
Hall, who claimed his maiden PGA Tour win in a play-off at the ISCO Championship in 2024, carded a bogey-free round. He chipped in for an eagle at his 15th hole alongside five birdies.
New Zealand's Ryan Fox holed a putt of more than 91 feet for a birdie on his 14th hole en route to an opening 68, one behind England's Aaron Rai, who is the highest-ranked player in a field devoid of stars.
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