MEXICO CITY • World No. 1 Lydia Ko beat hometown favourite Ana Menendez 3&2 on Thursday to launch her campaign at the LPGA Lorena Ochoa Match Play, where sisters Ariya and Moriya Jutanugarn set up a second-round duel between themselves.
New Zealand's Ko, who was forced out of last week's Texas Shootout with an eye infection, was the first winner of the day in the tournament that switched from its former strokeplay format this year.
She seized the lead with a birdie at the par-five second, and was able to take advantage of some miscues by Menendez - who won two holes with birdies but never got ahead.
Ko won the 14th with a par to go 3-up and sealed the win when they halved the 16th with birdies.
"Hopefully, that last birdie is good momentum going into tomorrow," Ko said. "Playing with a hometown girl (who is) one of the favourites, I knew that it was going to be a tight one.
"Matchplay is a different game to strokeplay. I enjoyed it, but you just never know."
Ariya, the top seed in her bracket, advanced with a 5&4 win over Amy Anderson while eighth-seeded Moriya beat Alana Sharp 2&1.
"We talked about (playing each other) after we saw the pairing," Ariya said. "We are lucky we hadn't booked a flight yet. We never know who's going to go back early."
The Thai sisters were paired together in the final round of the Texas Shootout, but Ariya said they had faced each other in matchplay only once, in an amateur event in Canada.
"We always try to be ourselves so she's probably going to say that she's going to go out there and play her best, so I say I'm going to play my best," Moriya said.
Belgium's Laura Gonzalez Escallon, the 16th seed in her bracket, notched the biggest upset of the day - a 2&1 victory over two-time Major champion Chun In Gee of South Korea.
Gonzalez Escallon won four holes with birdies, including the winning putt on the 17th.
"I am excited with this win - the odds were completely against me," she said.