O'Shea (23), an accountancy student at the University of Otago, won his first national senior men's title two years ago and confirmed his ability by winning the Oceania title in Cairns in September 2010 in a personal best time of 51.6sec.
A groin injury prevented him from defending his title in Dunedin last summer and he will be concentrating on the flat sprints this year.
"This season is a building block for me," O'Shea said. "I won't be running in the hurdles until next season. I will be building up my speed."
His goal next season is to qualify for the world athletics championships in Moscow in 2013 and he has worked hard to develop his speed under the direction of coach Brent Ward.
"I want to come out with all guns blazing next season to attack the 400m hurdles," O'Shea said.
He proved that the plan was working by dominating the men's sprints during the interclub athletics meeting at the Caledonian Ground on Saturday.
He won the senior men's sprint double in the 100m (10.96sec) and 200m (22.27sec).
O'Shea was a bit slow out of the blocks in the 100m and his club-mate Robert Jopp got the jump on him. It took him until 50m to hit the front and he powered away over the last 30m.
The minor placings were filled by Jopp, 11.25sec, and Sam Watson (Hill City), 11.91sec.
O'Shea will run the senior men's 200m and 400m at the national championships. He is ranked 20th in the 400m this season with his time of 50.64sec.
The 400m promises to be the most closely contested event at the championships with six athletes in contention for the gold medal.
Otago's Andrew Whyte (Hill City) has the fastest time of 46.91sec, recorded when he won the national secondary schools title at Wellington in December.
He is followed by Alex Jordan (Nelson) 47.24sec and Tama Toki (Auckland) 48.06sec.
Former national junior champion Matthew Robinson (Southland) moved himself up to fourth spot when he won the 400m at the Caledonian Ground on Saturday in 48.24sec. Robinson (20), a commerce student at the University of Otago, has a personal best time of 47.7sec.
Dean Rusbatch (Taieri) extended his men's aged 17 shot put record by 7cm when he won the junior men's shot put with 14.99m with the 6kg implement.
It was his third Otago record in the last three weeks.
He also had a personal best javelin throw by 72cm when he threw his implement 38.02m to finish second in the junior men's event behind Hamish Finnie (Hill City) who threw 38.44m.
Commonwealth Paralympics silver medallist Jessica Hamill (Southland) won the wheelchair shot put with 6.55m and the javelin with 12.87m.
Rozie Robinson (Hill City) was still recovering from the international road walk last weekend when she won the women's 3000m track walk in 13min 50.54sec.
At Hobart the previous weekend she finished seventh in the women's 20km road walk in 1hr 58sec and was second in the under 23 event.
The race was walked in temperatures of 38deg C and half the field of 59 pulled out with heat exhaustion.
