Both girls had entered four Show Hunter classes and expected to go up against large fields of more than 40 riders in their respective events.
While Show Hunter included elements of show jumping, Hannah said riders were also judged on their style, form and number of strides going into the jumps.
"And there's no numbers on the jumps, so you have to remember the course quite well," she said.
Rider and horse had to have a good partnership as it was important for the horses to take the correct lead when they changed direction heading into the fences.
"So you have to do lots of practice," said Ella who, despite not knowing what to expect as a competitor, had enjoyed attending previous HOY shows as a spectator.
"Watching the big classes jump is pretty cool," she said.
Hannah was eager for the competition to start but was not making any bold predictions about how she would fare.
"I'm excited and very nervous. Hopefully I can finish in the top 20," she said.
They may be first-timers at HOY, but the girls are certainly no novices when it comes to horses or equestrian competition.
They have been travelling away most weekends in the lead-up to HOY, and have competed at Foxton, Masterton, Wairoa and last year's Hawke's Bay and CHB A&P shows.
At their most recent competition at the Fielding Show last month, Ella's best result was a second place while Hannah was a little disappointed with a fifth.
"He [Matai SB] just wasn't listening to me that day," she said.
Mum Paula, who never competed at HOY but is also a former competitive rider, said the girls had not only grown up with horses, but had technically been riding since before they were born.
"I rode with both of them until I was about five months pregnant," she said.
The sisters will be among hordes of first-time entrants competing this week alongside top-name Olympic Cup showjumpers, seasoned eventers and dressage riders.
More than 50,000 people are expected through the Hawke's Bay Showgrounds gates this week, with the feature events such as the Friday Night Extravaganza, Woodford House Cross Country Brunch and Olympic Cup expected to draw large crowds this Friday, Saturday and Sunday.
HOY event director Dave Mee said entries for the equestrian events and pre-event ticket sales had both increased from last year's show with on-site camping and the Woodford House Cross Country Brunch almost sold out.
"It is fantastic to see the equestrian community and Hawke's Bay locals get behind the event," Mr Mee said.