The first record came in the morning, when Glassford clocked 2min 18.35sec to win his heat.
He went faster in the final and clocked another record time of 2min 17.10sec to win the open men's silver medal and collect 829 Fina points.
"I still can't believe it," Glassford said from Christchurch. "I swam a personal best twice and broke the record twice."
It was the best race of his short career and marked him as a swimmer with the potential to step up to the international level in the future.
He was competing at the New Zealand open swimming championships at the QEII Leisure Centre and finished runner-up to Glenn Synders (North Shore), who won the men's title in 2min 12.95sec.
Synders' time gained him 909 Fina points and a trip to the world championships in Rome.
Glassford (18) admitted being nervous as he stood on the blocks with the best senior swimmers in New Zealand.
"I was still shaking at the end of the race."
Glassford shifted to Dunedin from Alexandra nearly five years ago to study at Otago Boys High School and improve his swimming.
He trained with Duncan Laing at first and is now a member of the Osca squad that is coached by Gennadiy Labara.
All the hard work and long hours in the pool have paid off.
"You get out the results from the work you put in," he said.
Katie Kenneally (17), a food science and physical education student at the University of Otago, is another member of the Osca squad who won a silver medal last night.
It came in the women's 200m breaststroke when she finished runner-up to Natalie Wiegersma (Waverley, Southland), who clocked 2min 30.61sec.
Keannelly was close to her personal best time with 2min 34.19sec.
It was her second silver medal at the championships and adds to the five medals - four gold and one silver - she won at the New Zealand age group championships in Wellington last month.
Labara was proud of the Osca swimmers at the championships.
"They all qualified for either the A or B finals, which is a great performance for this young group of swimmers," he said.
Shane Patience, a member of Andy Adair's Waves squad, finished seventh in the 400m freestyle in a personal best time of 3min 57.95sec.
It was worth 820 Fina points.
