Phil Mickelson and Jim Furyk reached 12 under par to share the lead after two rounds of the US $5.5m (€4.2m) AT&T Pebble Beach National Pro-Am in California.
John Mallinger and Kevin Sutherland are their closest challengers at nine under, with Davis Love, Mark Hensby and Craig Kanada two strokes further back.
Furyk had the better round of the two leaders, shooting a bogey-free seven-under-par 65 at Poppy Hills, one of three golf courses used in the tournament – alongside Pebble Beach and Spyglass Hill.
Mickelson’s round at Pebble Beach was less convincing, featuring two bogeys as he finished with a 67.
The best round of the day was carded by Kevin Sutherland, who leapt from 58th to third after posting a nine-under 63 at Spyglass Hill.
England’s Greg Owen is tied for eighth at six under after shooting a 70 at Pebble Beach.
However, compatriots Luke Donald and Brian Davis are in danger of missing the cut.
Davis is tied for 95th at two over par and Donald, who finished tied for seventh last year, has shot rounds of 78 and 72 and is tied for 146th.