McLeish said: "I'm really delighted with Mauro. He was outstanding with his dribbling skills today. He was superb entertainment.
"You pick up contacts in the game who help to find you a player like Mauro. I had only seen him on video before I came here when I was manager of Scotland.
"I watched the FIFA Under-20 tournament in which he scored the winning goal in the final and you could see that he is a fantastic young talent.
"He has got a great future ahead of him and hopefully, if we retain our Premier League status, we can talk to Zarate about staying on for another season."
The margin of victory may have been greater but for the sending off of Franck Queudrue for holding back Benjani Mwaruwari.
McLeish said: "I'm just happy to win. We have too many draws at St Andrews even though we have played extremely well.
"The first-half performance was exceptional and we deserved to be leading at half time.
"The second goal made it comfortable for us but they we made a mistake which let City back into the game but I've got to compliment the team for their organisation after that and all round it was a satisfactory day."