Siyi, who made her debut at No5, showed no sign of nerves with a 6 and 4 win over Tracy Bary. Munchin, the New Zealand No1, defeated Emily Stenhouse 6 and 4 and Wenyung was just pipped by Sue Murray, who birdied the last to win 1up.
"It feels really good having two sisters in the team," said Munchin Keh of Titirangi Golf Club. "The team bonding is better than ever."
Pakuranga golfer Wenyung added: "It is quite nerve-racking for Siyi being her first Interprovincial.
"We didn't know how she would play," she said with a laugh, "but she did welltoday."
Siyi, also from Pakuranga, was not overawed.
"I was nervous on the first tee but once I got that hole done it was just another game of golf. It is good to know that I have my two sisters at one and two so they know my game and can help me out."
Siyi said the sibling rivalry was "definitely there" but strongest in her older sisters.
"We are quite competitive, but it is usually out of those two, I just hang out and give them surprises," she said.
Their parents, Michael and Elaine Keh, who caddied for Siyi and Wenyung respectively, said it was an honour to play a part in the special day.
"I am very proud of my girls to all play together. It is very exciting and a good experience for us [to be the first]," said Michael.
Phil Aickin, tournament director of the event, said the sisters' feat was probably a first in the amateur game and unlikely to be repeated.
