Villas-Boas admitted mistakes had been made but that he had helped both clubs achieve success.
"I achieved success in all of my teams," Villas-Boas, who was sacked by Tottenham in December after the 5-0 home thrashing by Liverpool, said.
"Tottenham had a good run in the Premier League. There were some mistakes, but the results are clear for all to see.
"As for my exit from Tottenham, there were contract issues there.
"I got an offer from Zenit last week, and the negotiations were fruitful. It was easy to agree, and I am glad to be here."
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