Sibanda was batting on 30 off 74 deliveries with six fours while Masakadza was on 19 off 44 balls with two fours and a six as the home team steadied the innings after the early dismissal of Tino Mawoyo.
The pair played both pace and spin with ease. Masakadza, known for his big shots, played cautiously but was quick to heave an over-pitched delivery from off-spinner Saeed Ajmal for the first six of the Zimbabwe innings.
Mawoyo played tentatively and edged an outgoing delivery for wicketkeeper Adnan Akmal to take a simple catch.
Earlier, Pakistan failed to add to its overnight score of 249-9 as Ajmal was bowled by pace bowler Tendai Chatara for 49, one short of his career-best score of 50.
Pakistan won a preceding three-game one-day series 2-1 and a two-game Twenty20 series 2-0.