The Nigerian received a second yellow card just two minutes into the second half at the Sukru Saricoglu, leaving the Biancocelesti to fight with 10 men.
"After the sending-off of Onazi, it was the start of another game," Cana told Mediaset. "They pushed a lot more and we defended ourselves."
Cana believes that the decision to penalise Stefan Radu for handball was "harsh", but remained hopeful of overturning the deficit at the Stadio Olimpico.
"We did quite well, but then there goal came from a penalty – and that seemed a little harsh," he added.
"With good spirit we can reverse the situation."
Dirk Kuyt wrapped up victory in the last minute in Istanbul.