A 54-hole cut is made and the final round is played at Pebble Beach.
The event is played across three courses - US Open rotational venue Pebble Beach Golf Links, Spyglass Hill and Monterey Peninsula Country Club.
With a 6-under-par 65 on a crisp, pleasing day, he shared top honors among the early finishers with four-time Pebble Beach Pro-Am victor Phil Mickelson, who also shot 65 at the Shore.
"I'm not going to chase them as hard as past year because you can get hurt doing that, you can get into some bad patterns". He played it off the beach back to the fairway, hit 7-iron to 10 feet and made the putt for a 69.
"I felt that I was practising better than I was playing, which is frustrating", the Greystones star said of his struggle to score well during the Middle East swing.
"I have the honour to play all three courses here and, just because of such attractive scenery, I couldn't even focus on where my ball was going", Choi said of Pebble Beach Golf Links, which is set on the famed Monterey Peninsula.
Pebble Beach is a happy hunting ground for the 48-year-old, who has won the event four times.
Most unusual was Mickelson avoiding the rough.
"I'm pleased with it (but) I definitely left some shots out there", said Johnson, four days removed from victory at the European Tour's Saudi International.
The South African was five under after only six holes with three birdies and a superb eagle at the second, but he did not manage another gain until the 18th as he settled for a share of ninth place with Johnson and Spieth.
"I'm very close to getting back to where I need to be".
Jordan Spieth has not lifted a trophy since the 2017 British Open and has drifted to 21st in the world rankings but the Texan says he would have had a good career even if he never wins again and that he will not go chasing results.