Osayomi's first international appearance for Nigeria came at the 2003 World Youth Championships in Athletics where she was a semi-finalist in both the 100 m and 200 metres. She began to compete in senior competitions the following year as part of the Nigerian 4×100 metres relay team. On her Olympic debut, her team came seventh in the women's final at the 2004 Athens Olympics and the team repeated that position at the 2005 World Championships in Athletics the next year. Osayomi proved herself individually at the 2007 All-Africa Games by taking a 100/200 m gold medal double before helping the relay team to the silver medal. On her world 100 m debut at the 2007 World Championships in Athletics, she made her way into the final round (finishing eighth) and set a personal best of 11.15 seconds in the heats. The Nigerian women did not reach the relay final on that occasion.