The Australian and his Kiwi teammate shot a combined 14-under total to be two behind leaders Nelly Korda and Tony Finau.
The tournament features 16 mixed teams with one male and one female player.
The teams played a scramble format Friday. Saturday's action will be foursomes (alternate shot) and Sunday will be a modified four-ball, where both teammates will tee off, then switch balls for their second shots and play that ball until holed.
Korda and Finau birdied the 18th to sign for their 16-under 56 at the Tiburon Golf Club in Florida.
They lead by one from Lucas Glover and Ireland's Leona Maguire, and Denny McCarthy and Megan Khang.
Korda and Finau were 13 under through 16 holes, but Finau sank a short eagle putt at the par-5 17th to move into a tie for the lead before they added one last birdie to eke in front.
"It was fantastic," Finau said. "We had a lot of fun and hit a lot of great shots. I watched a lot of great shots, a lot of great putts."
Korda was particularly impressed with the 9-iron Finau hit on the 17th that set up eagle.
"I got to see shots that normally I wouldn't let's say on the women's tour," she said. "That squeezer 9 you hit on No.17 was absolutely incredible. It's fun to see it first hand, as well."
Rising LPGA star Rose Zhang teamed up with Sahith Theegala this week and they birdied all but four holes for a 14-under 58.
They are tied with Canadian Nick Taylor and Ruoning Yin (China), the English pairing of Justin Rose and Charley Hull, and Day and Ko.
The Canadian duo of Corey Conners and Brooke Henderson posted a 13-under 59 to be tied eighth with Cameron Champ and US Women's Open winner Allisen Corpuz.
The pairing of Rickie Fowler and Lexi Thompson are at 12-under 60, along with Swedes Ludvig Aberg and Madelene Sagstrom.
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