"Rob told me that I had to take all three of the short turns if I was going to win," the 18-year-old Barton said after jumping clear in the fastest time of the jump-off to defeat Alex Ashman on Randal and Sara Rust on Bellamona.
It was the third major victory of the year for Barton, who had also won young riders' contests at Hickstead and the Festival of Show Jumping at Stafford on the nine-year-old mare.
Louise Whitaker, another 18-year-old, had earlier produced the first victory of the show for her well-known family when winning the Young Riders Stakes on the little Russian-bred Perepliot. Her father, John Whitaker, had been trying to buy the nine-year-old horse for a year before the Norwegian owner finally agreed to the sale four months ago.
Perepliot is only 15.1 hands high but he has the scope of a bigger horse. Whitaker, however, had already decided to ride the more experienced Livingston II in the championship, though she might have regretted it after two mistakes left her out of the jump-off.
Two other riders with Whitaker connections - Paul Barker, John Whitaker's former stable-jockey, and Billy Twomey, who is currently based with Michael Whitaker - had finished second and third behind Louise in the first class. Both reached the jump-off for the championship, in which they had a single error apiece to finish fourth and fifth.
Claudia Jordan took a bold short-cut on her pony, Classic Henna, to win the later Junior Foxhunter Championship by over four seconds.
HORSE OF THE YEAR SHOW (Wembley Arena): Young Riders Stakes: 1 Perepliot (L Whitaker) clear, 51.06sec; 2 Kildalton Lad (P Barker) clear, 53.21; 3 Boherdeal Clover (B Twomey) clear, 54.90. Squibb and Davies Junior Foxhunter Championship: 1 Classic Henna (C Jordan) clear, 31.46sec; 2 Gwaun Benjamin (L Riley) clear, 36.04; 3 CJS Kemosabi (V Jefferies) clear, 36.30. Fordyce Curry Young Riders Championship of Great Britain: 1 Valhalla (G Barton) clear, 30.80; 2 Randal (A Ashman) clear, 33.17; 3 Bellamona (S Rust) clear, 35.53. Thomas Bates and Son 7-year-old Championship: 1 Junior II (M Whitaker) clear, 33.21sec; 2 Claydons Peter Pan (G Luckett) clear, 35.30; 3 Exander (M McCourt) 4 faults, 33.78.