Robert Allenby's lead at the WGC-CA Championship was shattered by a double bogey.

On the opening day Allenby pitched in for an eagle and had six birdies to stand eight under par and four clear after 12 holes, only to bogey the final four holes.

His ace today came with a fairway wood at the short 13th, his fourth hole of the day, and birdies at the 10th and 14th took the Melbourne golfer to eight under again.

This time he shared top spot with South Africans Charl Schwartzel and Ernie Els, but on the 372-yard 16th Allenby drove into sand, duffed a pitch into another bunker and then missed from under four feet.

Second round tee-off times had been brought forward nearly three and a half hours because of the threat of thunderstorms and Els birdied four of his first seven holes.

Compatriot Schwartzel, the overnight pacesetter following a 67, resumed with a 10-foot eagle putt at the long first and then birdied the fifth.

The 25-year-old, twice a winner in his home country already this year, had been the only player in the 68-strong field not to drop a shot yesterday and remained bogey-free after 24 holes.

Padraig Harrington and Ian Poulter became further victims of the treacherous 467-yard 18th, however.

The hole was ranked the second toughest on the US Tour last season and after 18 balls found the lake on day one, Harrington and Poulter added to the total for the week by hooking their drives into the water.

Both escaped with bogey fives, leaving Harrington three under and still entertaining hopes of getting back in touch, but World Match Play winner Poulter was down on three over in joint 57th.

His back nine contained four bogey fives, two par fives and three threes, the last of them a birdie on the 17th.

"I've never had nine holes without a four," he said as he headed to the outward half.

Defending champion Phil Mickelson was alongside Harrington in joint 13th spot on three under, but Paul Casey had slipped back to two under and Luke Donald to one under. Both were one over for the day after nine and 10 holes respectively.

Yorkshire's Simon Dyson improved to one under with a birdie at the 11th, while Ross Fisher was level par, Lee Westwood and Ross McGowan one over, Rory McIlroy five over and Oliver Wilson six over.