"I was absolutely gutted about that because he was jumping so well and would have been in with a chance," said the 31-year-old.
But today it all came together for the two-time Lady Rider of the Year.
"This is such a special win. We couldn't have had a better start really. I thought we may have been in for a chance of a ribbon, but not the win," she said. "It was a strong and big field - the biggest I can remember for a long time."
But she had plenty of praise for Laplanche.
"He did such a superb job. It was not huge out there but it was fair enough."
Tinapai is known for his tricky behaviour and Fell said while he was "an absolute lunatic" when she worked him this morning, he had his game head on in the afternoon in the warm-up.
"I knew straight away it would be a good day. Sometimes you need a little luck in this game."
Tinapai, who has been with Fell for 12 years, had just one warm-up show heading into yesterday. She will probably start him at the next round at Mystery Creek early next month.
Fell would also like to win a third Lady Rider crown at the Horse of the Year Show.
"I know it is a little greedy to want one more, but that would be a dream to pull off."
With a two and a-half hour drive home, there was no time for celebratory drinks but Fell thought she would treat herself to McDonald's and a frozen coke.
In the opening round of the class, just four combinations left everything in place - first-timers Lily Tootill (Auckland) aboard Ulysses NZPH and Rachel Malcolm (Cambridge) on Equador MVNZ, along with Maurice Beatson (Dannevirke) on Conyers and Fell.
Thirteen of the 17 starters, who scored eight faults or less in the opening round, came back for the second.
Clears were a little more prevalent in the second round, coming from Beatson and Schimmel Warrior, Brooke Edgecombe (Waipukurau) on LT Holst Aunty Annette in their first World Cup start, Helen McNaught-McFarlane (Taupo) aboard Carnutelabryere and multi series winner Katie Laurie (Mystery Creek) on Dunstan Casebrooke Lomond, who was having his first crack at this level.
Laurie and her striking grey stallion, Dunstan Casebrooke Lomond, won the prize as the best presented at the horse inspection before the class.
It was a field that showed the depth New Zealand showjumping has coming through, with plenty promised for the coming World Cup rounds.
The next round is at Mystery Creek in early November. The series runs over six rounds, with the best four to count, and the overall winner has the opportunity to represent New Zealand at the world final in the United States next year.
In the Equissage Pony Grand Prix, just Ally Carson (Putaruru) aboard Tony The Pony and Emma Watson (Morrinsville) on Fun House came through to the jump-off.
Watson was out first on the former Pony of the Year and looked well on course to go double clear when a tight turn proved too much for the lovely grey and they finished with four faults at the second-to-last fence, coming home in 36.93 seconds.
Carson just had to leave everything up but it wasn't to be with the first of the double coming down.
Despite picking up the speed, they finished just short, with four faults, in a time of 38.75 seconds.
