McDonald (15), a year 11 pupil at King's High School, and Mawhinney (15), a year 11 pupil at Dunstan High School, were the top athletes in the under-16 grade, conquering not only some top-class competition but extremely blustery conditions.
Just an hour after winning the 400m in a personal best time of 51.70sec, McDonald was the only athlete to clear 6m in the boys 14-15 long jump. Into the teeth of a strong head wind during his three rounds of competition, he cleared 6.04m.
McDonald will also savour his result in the 100m hurdles, where he dead-heated with national secondary schools champion Patrick Taberner (Southland), both athletes credited with a winning time of 14.75sec for the second heat.
McDonald was back in the thick of the action as a member of the winning Otago under-16 medley relay team alongside Jacob Granger, Matthew Ogle, Oli Chignell and Schuyler Orr. McDonald's 800m run over the middle stages set Otago up for victory with a time of 3min 57.71sec.
Mawhinney won the girls 14-15 high jump, clearing 1.65m, but it was her triple jump victory that caught the eye when, running into a -4.2 head wind, she leapt 11.28m.
With barely time to catch her breath, she was involved in a tense three-way photo-finish in her heat of the 200m, in which she finished third, in 27.44sec.
Mawhinney is now focusing on the high jump and triple jump for the national championships in Wellington in March.
While her progress in the high jump has remained static this season - her personal best of 1.68m was established 12 months ago - her triple jump performances have been good. She started the season with a personal best of 10.98m, and before Saturday's triple jump competition, had increased this to 11.17m.
Saturday's meeting had a record-breaking start when Hinewai Collins (Southland) broke her own Southland girls under-17 record in the hammer throw, with a distance of 38.56m.
Otago's Libby Jones won the hammer competition with her throw of 41.07m. Jones also won the under-18 javelin with a throw of 22.45m, and under-18 shot put with a distance of 12.41m.
Nelson Maina (15), of the Queensland Development team, had all heads turning towards the under-16 high jump when, after clearing 1.9m, he opted for the height to increase to 1.96m.
Despite the crowd getting in behind the talented year 10 Brisbane State High School pupil, with a supportive hand clap in his preparation and run-up, Maina narrowly missed the mark on his third attempt as the bar caught his lower right leg as he descended towards the mat.
With a personal best of 1.95m, Maina has his sights set on the world youth championships in Colombia later this year.
