Ko moved past Inbee Park, who had been No. 1 for much of the last two seasons. Stacy Lewis is ranked third.
"It's history," said Lewis. "It's never been done.
"I can't say I'm surprised. It was just a matter of time. She's playing some great golf right now and she's confident. She's rolling in putts and it's good. She's a good kid and a good person to see at the top of the world."
[Complete Rolex Rankings]
Ko will tee it up at this week's Pure Silk-Bahamas LPGA Classic in a field of 120 players. She has five wins and 23 top-10 finishes in 43 LPGA events.
|WHEN THEY REACHED NO. 1|