World under-23 200m champion Arnott finished third in a combined ambulant 100m in a time of 11.58 seconds.
The 18-year-old was only beaten by 2012 Parlaympic champion Jonnie Peacock and visually impaired star Zac Shaw.
Arnott, who in IPC events competes in a different category to Peacock and Shaw, will run in the 200m on Sunday.
Meanwhile, Arnott’s City of Plymouth colleague Shayea came fifth in the women’s wheelchair 100m.
Sayea clocked 19.91 seconds in the heats before finishing in 20.21 in the final not long later.