McCarron, the 1997 champion, and DiMarco both shot five-under-par 67 in poor morning conditions at the Sugarloaf TPC.

However, both players will both be aware that defending champion Phil Mickelson lies only one stroke behind after he carded 66 in the afternoon.

McCarron and DiMarco were at nine-under 135, Mickelson was alone on 136, while Dennis Paulson (65) and Japan's Kaname Yokoo (69) were two shots behind.

World number three Ernie Els, who was six over par after nine holes of the first round, continued his comeback with a 67 that left him six strokes off the pace.

It was his first sub-70 score in 11 rounds.

Following Thursday's washout, the PGA Tour scheduled 36 holes for Sunday in an effort to finish the tournament on time.

The field was reduced to 53 players for the final two rounds.

If bad weather halts play on Sunday, the event may yet finish on Monday, although many players are reluctant to stay for a Monday finish, especially with the Masters starting in Augusta on Thursday.

Mickelson was excited at the prospect of playing 36 holes on Sunday: "At the U.S. Open, they used to play 36 holes on Saturday.

"I think it will be a great opportunity for the players of today to experience what it was like then," he added.