Viktor Hovland jumped into the outright lead at the halfway stage of the Farmers Insurance Open, with Jon Rahm among six players tied for second on a heavily-congested leaderboard.
Hovland broke free of the logjam at the top when he holed from seven feet on his final hole to cap a superb 65 on the South Course at Torrey Pines shortly after play had resumed following a suspension due to hailstorms and the threat of lightning.
Rahm birdied three of his last four holes for a 67 over the easier North Course as he became the first player to post eight under, a score matched by Adam Scott, Tony Finau and overnight co-leader Patrick Reed.
But Rory McIlroy struggled to get to grips with the pace of the greens on the North layout, while his long game was a little more wayward than day one, although he kept himself within four shots of the lead despite disappointing 71.
Hovland, widely tipped to make his Ryder Cup debut later this year, made light of the difficulty of tackling the South Course in conditions much cooler and wetter under foot than day one, and he got off to a great start with birdies at three of his first five holes.
The young Norwegian responded to a bogey at 15 with further gains at 16 and 18, and he added three more birdies over the front nine to take sole possession of the lead heading into the weekend having had a couple of weeks practising in the cold in Oklahoma.
"It's been really cold, so I've had probably three, four layers on practising and I think that's helped me for this week," said the world No 14. "It got really cold today and obviously raining and hail, so being Norwegian, I think that also helps.
"I just played really solid and made some putts. Playing a tough course like the South Course, you can't really fake it, especially in these conditions. Playing a hard golf course and then playing well, that I think is what gives me the ultimate kind of belief that I played really well."
Rahm added plenty of value to his prototype putter in a supreme performance on the greens on the North, rolling in an early 50-footer for birdie and blotting his card only once after finding a fairway bunker with his tee shot at the 13th - his fourth.
The Spaniard's grandstand finish ensured a place in Saturday's final group as he chases a second win at Torrey Pines having claimed his maiden PGA Tour title with his memorable 65-foot eagle putt on the 72 hole four years ago.
Scott got to nine under when he drained a 20-foot putt for eagle at the sixth - his 15th - on the South before two straight bogeys in the worst of the conditions saw him relinquish the lead, but he did close with a birdie at the ninth to card a 69.
Rahm and Scott were joined on eight under by Finau (67), Lanto Griffin (70) and Ryan Palmer (70), while Reed battled hard to grind out a 72 as he completed the tie for second place.
Alex Noren had shared the overnight lead with Reed after they posted 64s, and the Swede fought back well from a bogey-bogey start on the South with three birdies in four holes only to begin the back nine with three consecutive dropped shots.
Noren parred in for a 74 to stay at six under, with McIlroy one further off the pace after he was once again kicking himself for failing to build on a bright start for the second day running.
Having birdied two of his first three holes, McIlroy bogeyed three of the next five and struggled to get the putts to drop on the front nine until taking advantage of the par-five ninth, a birdie getting him into red numbers for the second day.
Phil Mickelson, meanwhile, looked set to miss the cut when play was suspended late in the day with the veteran left-hander two strokes outside the mark with only two holes remaining, but he returned to birdie 17 and 18 on the South to make it through to the weekend.