Brayan Leon struck twice late in the first half to cut Pirates' lead at the summit to three points, with Sundowns still holding a game in hand as they chase a ninth successive league crown.
Pirates began with intent and forced Ronwen Williams into two excellent saves inside the opening 15 minutes. Deon Hotto's deflected effort was turned away, before Yanela Mbuthuma was denied from close range after meeting an Oswin Appollis cross.
The hosts threatened again when Patrick Maswanganyi looked set to race through on goal, only for Khulumani Ndamane to produce a decisive tackle.
That proved a turning point.
In the 37th minute, Nuno Santos picked out Leon with a precise diagonal pass and the Colombian finished superbly from a tight angle. Four minutes later, he struck again, stabbing home Aubrey Modiba's low delivery to put Sundowns firmly in control at the break.
Pirates responded immediately after halftime. Maswanganyi fired from range and his effort took a heavy deflection off Teboho Mokoena, wrong-footing Williams and pulling one back.
The game opened up as the Buccaneers searched for an equaliser. Mokoena nearly restored the two-goal cushion with a fierce long-range strike that forced a sharp save from Sipho Chaine, while Ndamane later saw a header crash against the crossbar.
Despite late pressure, Pirates were unable to create sustained chances. The defeat ends their 14-match unbeaten run across all competitions and dents their hopes of ending Sundowns' long-standing dominance.
Both sides now turn their focus to Nedbank Cup fixtures this weekend, but the title race has taken on fresh intensity.
Brayan Leon has made an immediate impression at Mamelodi Sundowns, and head coach Miguel Cardoso believes the striker's quick adaptation is a testament to both his quality and the club's supportive environment.
Mamelodi Sundowns coach Miguel Cardoso praised the character of his players after a hard-fought 2-1 Betway Premiership victory over title rivals Orlando Pirates.
Orlando Pirates head coach Abdeslam Ouaddou has admitted that his side paid the price for poor finishing after a costly defeat to Mamelodi Sundowns on Wednesday night.
Stellenbosch were held to a 1-1 draw by fellow relegation threatened side Magesi in the Premier League clash at Danie Craven Stadium on Wednesday.
