Competing in the second semi-final, the 20-year-old finished second with a time of 51.81 secs.
Maximila Imali from Kenya finished first in 51.52 secs.
The six other athletes who also made it to the final were Jamaican duo Stephenie McPherson and Anastasia Le-Roy. Others are Amantle Montsho and Christine Botlogetswe from Botswana.
Others are Australian Anneliese Rubie of Australia and India’s Hima Das.
The News Agency of Nigeria reports that Ajayi won gold for Nigeria in the 4X400m relay at the 2015 Africa Junior Championships in Addis Ababa, Ethiopia.
Also, Faith Obazuaye will be targeting her second win at the Games when she takes on India’s Vaishnavi Sutar today in the women’s TT6-10 singles Group 2.
Obazuaye beat Andrea McDonnell from Australia in straight sets 9-11, 9-11, 6-11 on Tuesday to advance to the next stage.
In the men’s TT6-10 singles Group 2, Temitope Ogunsanya, who lost in three straight sets to Theo Cogil from South Africa, will face Barak Mizrachi from Australia.
The country’s number one table tennis star Aruna Quadri will feature for the first time at the Games today when he competes in the men’s doubles round of 32.
Quadri missed out on the men’s team event due to illness but will partner 43-year-old Segun Toriola in the doubles event against Tomlison Simon and Watson Kane from Jamaica.
Also, Abiodun Bode and Olajide Omotayo will face the duo Khawaja Fahad and Rameez Muhammad from Pakistan in another men’s doubles round of 32 clash.
Triple jumper Blessing Ibrahim finished fifth in the final of her event on Tuesday. The 28-year-old had a leap of 13.48 metres, which was not enough to earn her a medal. Jamaican Kimberly Williams won gold with a leap of 14.64m.