Boyle was pushed hard through the opening 400m by Wellington's Robinson, with just two seconds separating the pair at the halfway point. But Boyle was able to maintain a steady pace over the latter stages of the race to power home and claim the national title in a time of 8:25.00.
While she was still eight seconds off her personal best and New Zealand record, Boyle said she was happy with her time at this point in her training. She was happier still for Robinson, who, like Boyle, is based over on the Gold Coast but trains out of a different club.
"Emma is improving every year and it is great to see her getting faster. It's going to be her first Olympics and it's fantastic to have another Kiwi in my event because it's not very often we qualify two people in one event and I think that's a sign we're really getting some depth in some areas."
Heading into the race Robinson's personal best time of 8:31.98 put her just under the qualifying standard, putting her under pressure to reproduce her best if she was to make the team for Rio. Robinson responded by knocking just over half a second off her entry time - though she admits she hoped to go faster.
"I was confident of [qualifying] - I have a theory if you've got to believe you can or there's no point in doing it. I had hoped to go sub 8:30, but I'm happy to have qualified."
Both Boyle and Robinson are also chasing qualification in the 400m free on Wednesday.
The other big hope on the opening day was the North Shore's Helena Gasson, who emerged as an outside contender for an Olympic spot with an impressive swim in this morning's 200m butterfly heats, in which she shaved more than a second off her own New Zealand record set earlier this month.
But the 21-year-old, formerly from the Fairfield club in the Waikato, appeared to have left it all in the pool in the morning session.
Needing to knock a further half a second off her record in the finals to make the qualifying standard of 2:09.33, Gasson faded badly over the final 100m to finish in a time of 2:11.43 to not only miss out on Olympic qualification, but also the national title, with Wellington's Samantha Lee swooping in to take the spoils.
Glenn Snyders, chasing a third Olympic selection, picked up his 12th national title inthe 50m breaststroke with a time of 27.34 - only 0.25s outside his national record. The 50m is not an Olympic distance, but Snyders' first outing showed he is in good nick as he looked to the 100m distance on the penultimate day of the championship.