But the final on Tuesday night will be a race for the minor medals, and Boyle, Kobrich and Australian Jessica Ashwood look likely to battle for the silver and bronze. Around 8.5s covered those four swimmers in the heats.
Three other New Zealanders were in action tonight.
The youngest member of the New Zealand team, 15-year-old Hawkes Bay swimmer Bobbi Gichard, was fourth in her 100m backstroke heat and 26th overall in a time of 1:01.26, just .05s outside her season best.
That left her 26th overall out of 66. Her heat was won by Swede Michelle Coleman, who was 12th fastest into the semifinals in 1:00.55.
The fastest qualifier was Hungary's Katinka Hosszu who swam 58.78s.
American-based Corey Main was in the seventh and last 100 backstroke heat but found how hard the competition was when he was eighth in his heat in 54.51s, a mere .10s off his season best.
American Matt Grevers won the heat, and was second fastest into the semifinals in 53.21s, from Japan's Ryosuke Irie and Russian Evgeny Rylov.
Matamata's Matt Stanley had a second straight disappointing swim. After being well off the pace in the 400m freetyle 24 hours earlier, Stanley finished ninth in his heat of the 200m freestyle in 1:48.67, 1.5s slower than his season best, and national record.
The gold medal winner of the 400m, China's Sun Yang was the fastest qualifier in 1:46.00.