Bill Haas was facing a fight to retain his Northern Trust Open title after seeing his lead whittled back to one by the midway point of his final round in California. Haas had boasted a three-shot lead heading into the last day following his seven-under-par 64 on Saturday but the American was struggling to replicate that form yesterday.

The defending champion started with a birdie-bogey-birdie start but dropped shots on the seventh and eighth saw Haas reach the turn one over for the round. That also saw him slip back to 11 under for the tournament, and allowed four players to close to within one shot. Leading the charge was Hunter Mahan, who was four under after 10.

Also in contention on 10 under were Americans John Merrick and Webb Simpson, who were one under after nine, and Swede Fredrik Jacobson, who was two under.

Charl Schwartzel was on nine under along with Charlie Beljan.

Third-placed Ko reveals pro plans

Lydia Ko says she will turn professional in a couple of years after the 15-year-old New Zealander finished third in the Australian Open yesterday. "I've got a couple of years until I turn pro so hopefully I'll be able to get a little bit better," she said.

She finished behind British Open champion Shin Ji-yai and world number one Yani Tseng. Last Sunday, Ko became the youngest winner of a women's European Tour event in the New Zealand Open.