The 40-year-old captain made his comeback six months after rupturing his Achilles tendon.
"Zanetti has something special and you can see why he's a world class champion," Mazzarri told Sky Sport Italia.
"While the team was suffering, he came on for 10 minutes and gave everyone a sense of calm. To come back at his age after such a long lay-off and be immediately so confident, it's extraordinary. He's bionic!"
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