The 39-year-old, who has yet to win on the PGA Tour, fired a five-under-par 66 at the TPC Summerlin for a 12-under total of 130 in the first of four Fall Series events on the US circuit.
Wi, one of the best putters in the game, racked up six birdies and a lone bogey to join Venezuelan rookie Jhonattan Vegas (67) and American Kevin Na (63) at the top of the leaderboard.
Brendan Steele, who clinched his maiden PGA Tour title at the Texas Open in April, carded a 65 to end the day level with fellow Americans Tim Herron (66) and Kris Blanks (65) at 11 under.
Wi, an expert skier who also enjoys martial arts, was delighted to be in contention for the Las Vegas title after enduring an erratic 2011 campaign.
"I've had a pretty up-and-down year and I want to go out with a bang, make sure my game is ready for next year," he told reporters after recording two birdies in his last four holes.
The Korean, who failed to qualify for the final two events of the PGA Tour's lucrative playoffs earlier this month, has not previously been a huge fan of the Las Vegas Open.
"I've only been here once before in six years," said Wi, who has posted just one top-10 in 22 starts on the 2011 PGA Tour, a runner-up spot at the Colonial Invitational in May.
"I was here a few years ago and the scores were so low, I was kind of scared just coming over here. But I've played really well the last two days." Vegas, co-leader overnight with American rookie William McGirt, was happy to remain at the top despite not hitting the ball as well as he did during his opening 63.
"That's kind of why the round wasn't as good as yesterday," said the beefy Venezuelan, who won his first PGA Tour title at the Bob Hope Classic in January.
"But my putting's been pretty good ... hopefully I can continue that for two more days and we'll be right there." American Hunter Haas flirted with a magical 59 before posting the lowest round of the week — a sizzling 10-under 61.
"I know I had a chance (of a 59)," Haas said after finishing the round two strokes off the pace. "After I birdied the fifth hole, the par-three, I knew I had at least three good birdie opportunities coming in, and I screwed it up." Haas finished bogey-birdie-par-par after starting his round on the back nine.
"It's just a matter of making putts," he said. "That's all that matters out here." The cut fell at four-under 138 with Germany's Alex Cejka and former major winners Lee Janzen and Shaun Micheel among those missing out.
