Five-time major champion Phil Mickelson carded the lowest round of his career with a 12-under-par 60 at the Desert Classic in California.
Mickelson left a birdie putt at the par-4 17th just short before sinking a birdie at No. 18 for the 60.
It is one of three courses in use during the tournament, which includes the Nicklaus Tournament Course at PGA West and La Quinta Country Club.
Australia's Curtis Luck was alone in third after firing a bogey-free round of eight-under 64.
Adam Hadwin and Steve Marino were 13 under, and defending champion Jon Rahm was another stroke back with Wyndham Clark and Joey Garber.
Prior to the round Mickelson had said on Twitter he was excited to start the season but was "a bit rusty", and even after his flawless display he said he did not feel at his sharpest on the foggy and wet course.
"Sometimes you have those days where it all clicks", he told Golf Channel.
"You can make birdies there if you play well, hit good shots, and I'm starting to drive the ball a lot longer and straighter than I have in a while so that sets up nicely for that course", added Mickelson.
Ortiz had nine birdies and one eagle to jump a whopping 103 places - six of the nine birdies and the eagle were made after the turn.
"It was a fun day but I certainly did not expect this to be the case, but I'm also excited to start the year so I was fresh". "I feel like I can play aggressively with the way I'm hitting it off the tee".
The cut in the event comes tomorrow after 54 holes after all three venues have been played by the competitors before the event returns to the Stadium Tournament Course for Sunday's final round.
'And I hit a shot here or there and ended up making a putt and all of a sudden I was quite a few under par. Hadwin had a 66 at La Quinta, the course where he shot 59 two years ago.
"You only get to number one in the world by playing consistently good golf and that's always been my goal, to try and get the best out of my game week-in, week-out", Rose said.
He narrowly missed out on finishing 2018 as world No. 1 but reclaimed the ranking from Brooks Koepka last week after the American could only finish 24th at the Tournament of Champions in Hawaii.
Rose can expect stiff competition from Spain's defending champion Jon Rahm while two-time former victor Phil Mickelson is also in the field.