In a blanket finish Thornton threw Soleseifei over the line half a head in front of The Good Fight with Toms just a further head away in third.
Thornton was quick to pay tribute to the grit of her mount.
"She was entitled [to get tired] as I didn't get a great run and she was stuck out," she said.
"She was very brave.
"I was hoping to be forward but I couldn't get there. It wasn't until we were going down the back that I got a drag up from Sam Spratt [Justamaiz] in the three-wide train.
"Turning for home she was travelling super although it's a long straight to lead in, but she's tough."
The publicity-shy Lupton was swamped by her extended family and a large bunch of well-wishers in the Trentham birdcage as she struggled to take in what she had just achieved.
"It's pretty thrilling after Snowy did it with Kiwi and it's just lovely for the mare to do it too," she said. "She had a trouble-free run because nothing was falling back on her as she has had that the whole way through.
"She is a bit of a cripple and I spend a fair bit of time with her but she never goes a bad race and she tries really hard."
Soleseifei, who was a $26,000 purchase from the Rich Hill Stud draft at the 2014 Select Yearling Sale at Karaka, has now won five of her 29 starts. Rich Hill will offer a half-sister by first season sire Vadamos during the Book 2 session at the National Yearling Sale at Karaka that kicks off on Sunday.
- NZ Racing Desk