The first was the three-year-old Listed winner Surrey Thunder who was sold by Tuite Racing for 280,000 guineas after Mulcaster saw off underbidder Alex Elliott.
Surrey Thunder is officially rated 104 and has been placed at Group level on two occasions this year for trainer Joseph Tuite.
"Our prize-money keeps going up so we keep coming back," Mulcaster said of the success Waller has enjoyed with many horses purchased for him out of this sale by the New Zealander.
"He is a lovely style of a horse, looked well and has not been over-raced. Horses of his ability are difficult to get.
"We'll get him into the system at home and see where he fits in."
Surrey Thunder was sold by Surrey Racing, a syndicate run by investment banker Clive Hadingham and lawyer Steve Grubb.
"We are always looking for differing angles. This horse has been fantastic for us and the owners - we have travelled all around Europe with him.
"It is a balancing act between keeping them and selling them. This is the first horse we have had to sell at this level, it means we can go and buy again."
Mulcaster struck again when securing the Oasis Dream colt Imaging from the draft of Juddmonte Farms for 260,000 guineas.
The four-year-old is out of the Listed winner Mirror Lake and was victorious at Group and Listed level on three occasions for trainer Dermot Weld.
The top lot on the opening day was the Juddmonte Farms offering Sash knocked down to American buyers Red Baron's Barn and Rancho Temescal's Tim Cohen for 320,000 guineas.
"You have to pay to get quality. It is more than I wanted to spend but I didn't want to let him go either," said Cohen.
"This horse likes firm ground which is important going to California and he still gets all the conditions so he will fit into the program."
Sash was trained by Amanda Perrett and is the winner of three races over a mile, earning a Timeform rating of 101.
Cohen is a regular visitor to Tattersalls and the annual trip stretches back a generation beginning with his father Jed.
"I first came with Jed, who had set up Red Barons Farm," said Cohen. "He used to come here with his trainer Darrell Vienna.
"We had a bit of a break due to market forces and we were buying in South America, but we've been coming back for the last five years."
Cohen will decide on trainers at a later date. His buying team of Ed Freeman, Joe Miller of Kern Thoroughbreds and Alastair Donald of SackvilleDonald is set in stone
"I like to get the horses bought and then decide, but we have a great buying team - we work so well together and we all bring something to the table," added Cohen.
The popular Juddmonte consignment realised a total of 1,577,000 guineas for the 23 lots offered.
Autumn HIT Sale 2019 - Day 1 Statistics
Lots Catalogued: 433 (2018 425) +2%
Lots Withdrawn: 128 (119) +8%
Lots Offered: 305 (306) 0%
Lots Unsold: 40 (50) -20%
Lots Sold: 265 (256) +4%
Aggregate (gns): 7,696,700 (5,588,600) +38%
Median (gns): 13,500 (10,000) +35%
Average (gns): 29,044 (21,830) +33%
Lots Sold: 87% (84%) +4%