McPhail (22) burst out of the blocks and wound up good speed on the turn, momentum taking her down the straight to finish in 25.91sec, a personal best.
Her 200m win came just 40 minutes after she finished second in the 100m behind Larissa Dyke (Taieri). Dyke clocked 12.26sec, with McPhail second in 12.63sec.
Daniel O'Shea (Hill City) rubbed the sleep out of his eyes to record an impressive victory in the senior men's 200m.
O'Shea started well and showed good speed on the turn into the straight, stopping the clock at 22.31sec and holding off a strong challenge from William Mohammed (Canterbury), who recorded 23.49sec.
O'Shea (25) was competing in a Grand Prix meeting in Auckland on Saturday - he finished second in the 400m hurdles in 51.35sec - and checked in at Auckland Airport at 5.30am yesterday for a flight back to Dunedin.
He has meetings in Sydney and Melbourne over the next two weeks before the national championships, where he will contest the 400m and 400m hurdles.
Ben Anderson (Caversham) appeared to be always in control of the 800m, winning in 1min 52.86sec. Promising junior Sam Bremer (Hill City) was second in a personal best time of 1min 54.49sec, and Dave Catherwood (Ariki) third in 1min 58.61sec.
Dunedin's Nathan Baxter displayed a clean pair of heels in the Papatowai Challenge on Saturday.
Baxter made his intentions clear to the 300-strong field from the start and recorded the second fastest time on the 15km course of 52min 46sec. His old Ariki clubmate, Dougal Thorburn, holds the course record of 51min 31sec.
Baxter set a determined pace and threatened Thorburn's time until a strong headwind over the final 2km slowed him considerably.
Baxter (26), has made every post a winner since returning to competitive running a month ago, when he clocked 14min 58sec to win the Otago 5000m track title, and on the basis of Saturday's run, he will go into the harrier season as Otago's top-ranked winter athlete.
Following in Baxter's wake for second place was Peninsula Challenge champion Neale McLanachan, in 57min 39sec. Defending champion and Rotorua marathon-bound Jason Palmer was third in 58min 27sec.
The race for the open women's title was a hard-fought affair, with the Dunedin duo of Sasha Antunovic and Mel Aitken locked together until Antunovic hit the afterburners 200m from the finish.
Antunovic won in 1hr 5min 27sec. Aitken was second in 1hr 5min 35sec and Amanda Rowe third in 1hr 10min 36sec.
