Running in lane seven, Amusan won the second semi-final despite having a slow start.
She is now looking all fired up for Thursday’s final race and defend the title she won last year in Oregon.
Amusan was only cleared to run last week over an alleged breaking of the anti-doping rules but the Nigerian came through as a semi-final winner in 12.56sec.
She was pushed all the way by young Jamaican Ackera Nugent, who enjoyed an early lead before Amusan snatched victory at the finishing line.
The reigning NCAA Champion who clocked 12.60 seconds eventually settled for the 2nd position.