Brendan O'Neill of DSD and American visitor Mary Ballinger were the winners of the Sonia 5km in Dun Laoghaire.
About a thousand turned out to honour Ireland's most successful ever female athlete on the 20th anniversary of her world 5000m title in Gothenburg, Sweden.
O'Sullivan finished second woman and then turned back to cheer on the rest of the field.
In Trim, Peter Brandon Somba of Dunboyne was first home at the Braveheart Trail 5km in 15 mins 40 secs.
Slí Cualann's Deirdre Byrne was first woman.