The 24-year-old swam a good race to finish second behind world and Olympic champion and world record holder Rebecca Adlington of Great Britain in a new national record time of 8:25.91.
But Boyle, who finished eighth in the 400m freestyle final earlier at these Games, was realistic about her chances in tonight's final (NZT).
"I expect them to go a lot faster in the finals tomorrow so it's going to be a case of being in my own body and not caring where they are in relation to me," she said.
"I will probably need to go at least six seconds faster [to medal] and I really don't know if that's possible, so don't expect anything from me. I'm definitely happy with a new best time and getting into the final is amazing."
Boyle remains the only New Zealander to make a final in the pool at these Olympics, and she will feel tonight's swim justified her decision to withdraw from the women's 4x200m freestyle relay team who set a new national record yesterday but missed out on a place in the final - they probably would have qualified if Boyle had swum.
Daniel Bell finished fifth in his heat of the 100m butterfly in a time of 53.76 seconds, putting him 37th of the 43 swimmers and his place in the men's 4x100m medley relay team in jeopardy. Andrew McMillian recorded a time nearly half a second faster in an official trial recently and could join Glenn Snyders, Gareth Kean and Carl O'Donnell in the team.
Melissa Ingram's Olympics career ended on a "stink" note when she missed out on qualifying for the semifinals of the women's 200m backstroke by an agonising 0.03 seconds.
She was targeting a place in the last 16 but her time of 2:10.63 was pipped by Sharon van Rouwendaal of the Netherlands.
"Bloody hell, ah," Ingram said with a disappointed shrug of the shoulders. "It's heartbreaking but I gave it everything. I could barely get out of the water afterwards and I guess that's just sport for you. No excuses."
Ingram isn't retiring from swimming yet and will get back in the pool to prepare for the world short course championships but the 27-year-old who has competed at three Commonwealth and two Olympic Games is adamant she won't be around in Rio in 2016.
Whether that means the 2014 Commonwealth Games in Glasgow, Ingram was non-committal. "We will see," she offered.
