American Sean Crocker set the pace with a 63 that contained an eagle and eight birdies as around 120 sub-par scores were produced on the Torrance Course in benign conditions.
Law, who finished in a tie for third behind compatriot Grant Forrest in the same event 12 months ago, set up his promising start with a burst of five straight birdies on the front nine.
The effort came with Michael MacDougall, who works for Paul Lawrie’s Five Star Sports Agency, on the bag after Law’s normal caddie, Max Bill, fell ill on Wednesday night.
“He did a good job,” said Law of MacDougall, who helps look after the players managed by Lawrie and also runs events on the Tartan Pro Tour. “He was good. He’d caddied in a tour event before, so he knew what he was doing. We just had a great laugh out there.”
The 31-year-old took last week off after making that major debut on the back of his top-five finish in the Irish Open then also getting into the Genesis Scottish Open.
“I really enjoyed it, the pressure of it all,” admitted Law of playing in the 150th Open. “The biggest stage in golf, really. So it’s nice to come back and be in this area so soon after that week.”
Syme described his bogey-free performance as being “basically textbook” and reckoned he could easily have gone lower. He wasn’t complaining, though.
“I like it up here,” he said of the clifftop venue. “The guys are really good in letting me come up a couple of weeks ago for a couple of practice rounds.
“It’s not far from home, in my own bed for a change, which is nice. It’s weird, you forget I’m playing in a tournament this week when you’re in your own place.”
Scott Jamieson carded an eagle and four birdies as he signed for a 66, two less than defending champion Grant Forrest and last weekend’s Cazoo Classic winner Richie Ramsay, as well as Kiwi Ryan Fox, the highest-ranked player in the field.
“Pleased with the scoring, yeah, but I didn’t play too well today, to be honest,” said Forrest, who holed from 30 feet then 21 feet for successive eagles on his back nine. “Off the tee I was struggling a bit.
“But I dug in there, back-to-back eagles on six and seven was a big help. Four-under is good, I’ll definitely take that today.”
Crocker, a 25-year-old who was born in Zimbabwe but now lives in Florida, set up his score - he leads by one from a group that includes Spaniard Adrian Otaegui, who won the AXA Scottish Championship on this course in 2020 - with a burst that produced an eagle and four birdies.
“That was fun,” admitted the leader. “I don’t get too many days like that on the greens, but these ones just fit. They aren’t too slopey, not too linksy.”