Trio of golfers lead after opening round at Torrey Pines
The 27-year-old from Wolverhampton took advantage of benign golf conditions on the North Course to fire an eight-under-par 64 and finish the day alongside Americans Sam Ryder and Brent Grant.
Teeing off on the back nine, Rai made three birdies before the turn and then reeled off five birdies down the stretch to complete a bogey-free round.
Grant meanwhile made nine birdies and one bogey for his eight under.
Ryder's bogey-free round comprised six birdies and a brilliant opening eagle three on the par-five 10th hole.
"Definitely played great all around," Rai said afterwards. "Really drove it great off the tee, which is probably the most important thing.
"As soon as you miss the fairway here with anything more than a short iron it is very, very difficult.
"So that was key today, drove it very well. Hit a lot of real good iron shots and made a few putts around the turn there, so all in all a very good round."
Ryder said his opening eagle had laid the foundation for his low score.
"It was pretty stress-free, it was fun," Ryder said. "Always nice to get off to a good start in the round where you don't feel like you're kind of pressing or anything."
The trio are one shot clear of Brendan Steele, who fired a seven-under-par 65, and two in front of a cluster of seven players on six under.
Seven players are a further shot back on five under.
But there was disappointment for in-form Spaniard Jon Rahm, who struggled on Torrey Pines South Course with a one-over-par 73.
Rahm came into the tournament looking for a third win in his third straight start.
But though he made a steady opening-round start on the South Course, with a pair of birdies in the first five holes, he struggled to regain momentum after a double-bogey six on the par-four seventh.
Two more bogeys on the back nine left him two over before a birdie on 16 stopped the bleeding.
Rahm was left baffled by his costly double-bogey on the seventh, which came after he shot through the green into a hazard with his second.
"I've hit that shot 25 times in the past with the same wind and I've never seen a ball get pin high, I don't know what happened," Rahm said.
