Adams, using the 4kg shot, took the lead with her first throw of 19.54m.
There was a respectful hush before each throw until Adams egged the crowd on before her fifth attempt and she delivered with her biggest heave of 20.35m.
With only one legal throw to his name, Gill responded with a 21.01m effort and a huge cheer went up when the white flag was raised. However, Gill saved his best for last throwing 22.06m to finish and seal the win.
Avoiding defeat at the hands of a girl, albeit a world champion, was pleasing for Gill.
"Definitely guys never like to lose to girls, so it was good to beat her," Gill said.
The hulking 17-year-old was happy with his winning throw but questioned the red flags.
"Apparently I was clipping my foot on the rim during the spin and the umpire can only call what he sees, but we will be checking the video."
Gill had earlier won the discus with a throw of 60.44m into the teeth of an easterly wind. He then wandered down to the shot put ring and casually threw past the 20m mark with his first warm-up. He opted for the under-19 weight of 6kg rather than the Olympic 7kg.
"My first focus is the junior worlds in Barcelona where I'll throw the 6kg. I'll switch to the 7kg to prepare for the Olympics," Gill said.
Adams had to settle for second but was satisfied as she began her Olympic title defence. "It was my first competition of the season so I was a bit rusty but to land over 20 metres was a good start,' she said. "My goal was to get some good throws in but also come down and support the people of Christchurch. It was just great to see a big crowd getting up close and getting in behind us."
With the shot put showdown settled, the focus turned to another Olympic hopeful as Nick Willis contested the feature track race, harking back to the old days of grass racing and mile measurements.
In the two mile handicap, Willis was again pipped by American training partner Will Leer, who defeated him recently at Wanganui. Leer owed the win to his parents. He won in Wanganui on his father's birthday so needed to win in Christchurch on his mother's birthday.
Olympic hopeful Nikki Hamblin withdrew with a recurring Achilles injury.