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Nascimento has penned a new three-year deal with the Tshwane outfit.
The 34-year-old has appeared 57 times for Sundowns since joining the club, scoring nine goals in the process.
Sundowns also confirmed that Mkhulise has signed a five-year contract, after his breakthrough in the first team.
The 22-year-old made his first team debut in the club's MTN8 semi-final tie against Cape Town City.