World-number-one Jin-young Ko birdied the final hole to defeat Caroline Masson 1 Up on Thursday to remain unbeaten in the the group stage of the LPGA Bank of Hope Match Play event in Las Vegas. Ko lost 16 and 17 before recovering to squeeze out the win over her German opponent. The group stage continues on Friday, then 16 players will advance to the knockout round on Saturday. The semifinals and final will be on Sunday.