Gai Waterhouse and Adrian Bott were the heaviest-hitters on Day 4 at the Magic Millions Gold Coast Yearling Sale, landing the highest-priced lot of the sale and another seven-figure youngster who boasts bloodlines they know well.

A few hours before they paid $1.7 million for the session-topping filly by I Am Invincible out of Madam Rogue in partnership with a number of stable clients, they paid $1.3 million for a colt by Justify, the sire of their Magic Millions favourite Storm Boy.

The colt had dual appeal not only being by Storm Boy's sire but also out of the I Am Invincible mare Invincible Star, who Waterhouse and Bott trained to win the Group 3 Ottawa Stakes on debut and finished second in the Group 1 Coolmore Stud Stakes.

"We know mum very well and we're starting to get to know a little bit about the progeny of dad as well with Storm Boy obviously going into the Magic Millions," Bott said.

"Invincible Star was such a sharp horse. We had her and she won first time out up the straight at Flemington – she was so quick – and we had her lined up for an Everest at one point and she just went down a nose in the Coolmore.

"She was the fastest filly of her generation and we've seen what Justify is starting to do down here, so it seemed a nice mix."

The Invincible Star colt is the most expensive lot to date by Justify at this year's sale and he was one of two big lots in the first half of Day 4.

Just nine lots earlier, Peter Moody and TFI paid $1.4 million for a filly by Snitzel out of In Times Of War, who is the dam of this year's Breeders' Plate winner Espionage.

Justify won the Triple Crown in America, but Storm Boy and one of last season's top two-year-old fillies Learning To Fly is evidence he can throw an early runner and Bott said the Invincible Star colt would be given the chance to prove his precocity.

"We're always looking for horses that can potentially get us back here next year with the ultimate aim being looking for Golden Slipper winners with colts out of this sale," he said.

"In saying that, he's a colt with some nice scope about him and I think there's a lot more options for him.

"We're going to see a lot more from him going past his two-year-old career as well."

Waterhouse and Bott's initial big purchase came a little more than 24 hours out from the Magic Millions 2YO Classic, for which Storm Boy is $2.40 favourite, and Bott is happy on race eve.

"He's had a great week, he looks fabulous, so we're looking forward to Saturday," he said.