Pebble Beach - Australia's Matt Jones fired eight birdies in a six-under-par 66 on Friday to share the halfway lead with former champion Brandt Snedeker at the $6.8 million Pebble Beach National Pro-Am in California.
Snedeker and Jones finished 36 holes at 12-under-par 131, one stroke ahead of overnight co-leader Justin Hicks.
John Daly, who started the day one off the lead, couldn't find a birdie over his last 11 holes and fell six shots adrift. First-round co-leader J.B. Holmes also struggled and found himself six back and in danger of missing the cut.
The field will be reduced after Saturday's third round, after every player has tested each of the three courses in use over the first three rounds - the par-72 Pebble Beach Golf Links, par-72 Spyglass Hill and par-71 Monterey Peninsula.
Australian Jason Day, who vaulted to fourth in the world with his playoff win at Torrey Pines on Sunday, made a big move toward the top, carding a nine-under 62 at Monterey Peninsula to join a group tied for 14th on nine-under par despite being unwell.
Snedeker had five birdies without a bogey in his five-under 67 at Spyglass Hill.
The 34-year-old American won the Pebble Beach crown in 2013 and went on to win the Canadian Open the same year, but hasn't added to his six US tour titles since then.
Jones is seeking to add a second US title to the Houston Open crown he captured last year.
Hicks fired a three-under 68 at Monterey Peninsula and was alone in third on 11-under 132.
Ten players were tied at 10-under: Jon Curran, Billy Horschel, Charlie Beljan, Michael Putnam, Chez Reavie, Daniel Berger, Alex Prugh, Will Wilcox, David Hearn and Chesson Hadley.
Day's move into contention was all the more impressive since the 27-year-old thought a stomach ailment might prevent him from teeing off.
Day said he thought he caught a bug from his young son Dash, who was so ill earlier this week that his parents took him to a hospital emergency room.
"He had some stomach problems and he was throwing up," Day said. "And then he gave it to my wife and then my wife gave it to me. So I didn't think I was going to play today, especially 30 minutes before my round because I was feeling pretty awful."
Day shook it off to post a 62 that included an eagle and eight birdies with just one bogey.
"To be able to shoot nine-under out there with how sick I was, thinking about pulling out, was pretty special," Day said.
Leading second-round scores on Friday in the $6.8 million Pebble
Beach National Pro-Am on the par-72 Pebble Beach Golf Links, par-71
Monterey Peninsula, par-72 Spyglass Hill (USA unless noted):
131 - Matt Jones (AUS) 65-66, Brandt Snedeker 64-67
132 - Justin Hicks 64-68
- Charlie Beljan 70-63, Michael Putnam 69-64, Chez Reavie 67-66, Daniel
Berger 67-66, Will Wilcox 66-67, David Hearn (CAN) 67-66, Billy
Horschel 68-65, Chesson Hadley 64-69, Jon Curran 69-64
134 - Alex Prugh 66-68
134 - Nick Watney 65-69, Jim Furyk 64-70, Pat Perez 66-68, Jason Day (AUS) 72-62, Daniel Summerhays 67-67