A long day filled with sunshine and mud balls ended with Vegas in the penultimate group playing the best golf hardly anyone saw.
A briefly energised crowd had mostly left when Vegas blazed his way to the finish with five birdies on his last six holes, ending with an 18-footer on No.8 and a 25-footer on the rugged ninth.
It was Vegas' best score in 45 rounds playing the majors.
Despite being a four-time PGA Tour winner, the 40-year-old has never finished in the top 20 in a major and hadn't qualified for this one in three years.
He now has a two-shot lead over Ryan Gerard, the PGA Tour rookie who grew up in North Carolina and was the only other player to reach seven under until bogeys on his last two holes, and Australian Cam Davis, who matched his 66.
"I got lucky that I was able to tee off very late and the course obviously is drying very quick," Vegas said after becoming the first Venezuelan to hold the lead at the end of any round at a major.
"So I was able to take advantage a little bit of those conditions at the end of the day today.
"But obviously a solid round from beginning to end. Good way to start."
The biggest crowds belonged to the top three in the world, and it wasn't nearly as inspiring as four of the last five majors they have combined to win.
Masters champion Rory McIlroy didn't make birdie over his last 12 holes and had nothing to say about that after a three-over 74 sent him straight to the range.
Scottie Scheffler and defending PGA champion Xander Schauffele had plenty to say about mud balls on tee shots, particularly on the 16th hole that sent both to double bogey.
Scheffler at least holed two shots from off the green - one for birdie, one for eagle - and finished with a 6-iron from 215 yards to three feet on No.9 that sent him to a 69.
For the first time in at least 30 years, the top 10 scores after the opening round of a major did not include anyone from the top 10 in the world ranking.
Instead, Vegas stole the show as Scheffler, typically, posted the best score of the top-10 stars.
