Jeremy Brockie opened his Sundowns account after 11 minutes with a great left-footed volley from inside the box for his first competitive goal in Brazilian colours.
The goal seemed to spur Sundowns on and allowed them to dominate and threaten the Free State Stars goal.
Soon after, Sundowns were then awarded a penalty after Bangaly Keita bought down Aubrey Ngoma. Sirino stepped up to convert the spot kick to make it 2-0 in the 24th minute.
Three minutes later, Sirino grabbed his brace with a stunning long range shot that left Badra Sangare with no chance.
Ten minutes before halftime, Harris Tchilumbu pulled one back when he quickly tapped in Judas Moseamedi’s low cross from close range, 3-1.
Ten minutes into the second-half, Badra Sangare produced a spectacular double save as he denied Brockie and Ngoma goals from close range.
As Sundowns upped the tempo, Sirino set-up Brockie who wasted a wonderful opportunity to grab the fourth goal as he shot straight at Sangare on 66 minutes.
Sundowns controlled much of second half proceedings while Ea Lla Koto struggled to get past the home teams defense.
Sirino was on the end of everything positive for Sundowns, this time striking a long range effort saved by Sangare with 80 minutes gone.
Stars finished the game with ten men after Nyiko Mobbie was sent off for a second bookable offense in the 90th minute as the match ended in victory for Sundowns.