Walter Mazzarri was axed on Friday to be replaced by Mancini.
Thohir said: "Moratti helped a great deal, because he is someone who knows football well and already knew Mancini for a long time. Roberto is the best choice we could've made.
"He is one of the best Italian Coaches, in fact I'd say the best. He won and achieved great things everywhere. His career speaks for him.
"Plus there is another reason: he knows what Inter means, has been part of our family and cares about these colours. We spoke on the phone. He is very motivated and his quality is not up for debate. I'll meet him in person next week.
"Mancini knows Inter. We could not afford a Coach who was starting from scratch, who needed a year to get the results we wanted. I asked him to confirm our status in Europe for next season and to secure Champions League qualification as soon as possible.
"We are Inter and we have to stay in Europe. We changed Coach because the next three games will be very important. With his experience, Mancini can help us."
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