The Englishman, like Spain's Rahm, headed out on the North Course at Torrey Pines and carded a nine-under-par 63 after eagling his first hole.

"I'm really happy with that," said Rose, who will play the South Course on Friday. "I felt really comfortable and gave myself plenty of opportunities."

Three-time major champion Jordan Spieth is also in contention at seven under.

"To shoot nine under and take advantage was really important," Rose added on Sky Sports.

"The design of the South Course is fantastic and the modification to the north is fun now. When you enjoy being somewhere it normally shows in your game."

Tiger Woods, who won the last of his 14 majors at Torrey Pines in 2008 and has collected 10% of his 80 PGA Tour titles at the venue, headed out on the historically more difficult South Course.

The former world number one, whose US Open triumph was part of a four-year undefeated streak at the California course, began his day with a bogey but recovered to post a two-under-par 70 that included a birdie at the last.

Northern Ireland's Rory McIlroy will also play the North Course on Friday looking to improve on his opening-round one under par.

McIlroy made his second birdie of the day at the par-five 18th to recover from a bogey two holes earlier.