Rylee Sheehan (Te Aroha) and Bandito NZPH rode clear but had four faults in the first round.
Fastest time of the second round went to Linton aboard his eight-year-old mare but they paid for their speed with two rails down in their 43.29-second effort and had to settle for fifth.
Newsom stopped the clock in 46.01 seconds for second and Simon Wilson (Waipukurau) and McMillans Ariados were third on four faults and a second round time of 45.38.
Sheehan was fourth on four faults and a time of 49.02.
But the day belonged to Fitzsimon and her eight-year-old bay, who last weekend competed in the FEI World Cup New Zealand Series final in Auckland.
Her plan coming into the class had been for two nice rounds after a “challenging” weekend at the World Cup final.
They started the second round slow and steady but soon picked up pace to clock a clear 45.3-second round for the win.
“We changed our plan on Sunday night and decided to come to Gisborne for a confidence-building outing,” said 30-year-old Fitzsimon.
“He was great out there and after this show will have three weeks off until the Takapoto Estate Show Jumping.”
Fitzsimon, who comes from the town of West Melton near Christchurch, had plenty of praise for Duffy's course.
It jumped really well, produced some nice rounds and was a good lead-in to tomorrow's Equestrian Sports New Zealand horse grand prix.
“Gisborne has a really nice atmosphere and good vibe. The ground is awesome out there,” said Tegan, tipping her hat to the hard-working committee for its efforts.
In October she and her top horse, Windermere Cappuccino, won the horse grand prix at the Poverty Bay Spring Show.
Yesterday's main class rounded out another great day in the saddle for Tauranga teen Newsom who took the quinella in the open horse 1.2m for horses seven years and under.
She won aboard Charmed Escudo MSNZ and was second on Distinction MSN.
Newsom and Caretino Jewel were also fourth in the open horse 1.2m.
Newsom is enjoying a purple patch with her team.
She and Caretino Jewel also won the best presented combination at the FEI CSI1* horse inspection.
Local riders enjoyed success on the opening day of the champs, which for the 30th year in a row are being sponsored by Larsen Sawmilling
Sofe Gaddum and Sentra won the open horse 1.1m class; Kirsty Harnett and Ngahiwi Prince were second in the open horse over seven years 1.15m jump; and Larina Dolman and Floriant DHU were second in the open horse 1.3m.