R1 LEADERBOARD US unless stated -7 S Appleby (Aus) -6 J Daly, E Els (SA), B Wetterwich -5 S Lowery, O Uresti, T Purdy

The Australian carded a seven-under 63 to move clear of chasing trio Ernie Els, John Daly and Brett Wetterich.

World number one and Masters winner Tiger Woods was six shots off the pace as he battled to 69 while Vijay Singh had a mixed round to finish on 68.

Luke Donald was the best Briton on two under with Justin Rose one shot back.

Appleby was relieved to be back at his best after seeing his form dip since winning the season-opening Mercedes championships.

"I'm probably three or four tournaments down in my schedule over this year," said Appleby, who took time out from the PGA Tour after the birth of his son in January.

"I played okay last week but didn't really seem to get much out of my golf. Today I managed to aim the putter in a better direction."

I just couldn't make any putts - my lines are just a little off Tiger Woods

World number three Els also returned to form on his first appearance on his first Tour event since finishing 47th at the Masters.

The South African carded a bogey-free round of 64 on the Las Colinas course.

"I want to play better over here," said Els. "I felt comfortable over the ball and I'm feeling good."

Daly, who was playing among a group of players on the Cottonwood Valley course, was also set for a flawless round until he bogeyed the 18th.

Woods and Singh both endured mixed rounds. The American only had two holes under par - a six-foot eagle on the seventh and a 30-foot birdie on the 18th.

"I just couldn't make any putts," said Woods. "My lines are just a little off."

Victory for Singh in Texas would see him take over the world number one spot from Woods.

But the Fijian virtually cancelled out the good work in sinking seven birdies by dropping five shots.

World number four Phil Mickelson had an uneventul round to join Woods on 69 while South African Retief Goosen settled for an even 70.