The Springboks led 45-0 at halftime after blowing their hosts away in the opening period, but were nowhere near as clinical after the break.
The scoreline provides a significant boost to their points difference in the Southern Hemisphere standings as they moved five competition points clear of New Zealand, who were due to play Scotland later on Saturday.
The Springboks face tougher assignments away to France next weekend and Ireland a week later, but this was another accomplished display from Rassie Erasmus' side, who were at times untouchable in the first half.
South Africa were forced into a late change when lock Salmaan Moerat was injured during the warm-up and replaced in the starting XV by Lood de Jager, with Franco Mostert coming onto the bench.
The Springboks started by camping in the Italy half and Sacha Feinberg-Mngomezulu's penalty after five minutes gave them the lead.
South African-born Ross Vintcent was an early replacement for Italy after flanker Alessandro Ortombina left the field for a head injury assessment (HIA).
Feinberg-Mngomezulu's dummy created a gap in the home defence and the flyhalf raced over in the corner before converting his own try to make it 10-0.
It was all South Africa in the opening quarter and they scored a second try as scrumhalf Morné van den Berg burrowed over from close range after Italy had successfully stopped a driving maul.
Malcolm Marx then barged over as sustained pressure earned the visitors penalties and territory, with the Springboks making their visits to the Italian 22 count.
Twenty minutes in, South Africa led 24-0 and Italy had barely had their hands on the ball.
The hosts lost wing Monty Ioane to an HIA and when Feinberg-Mngomezulu's brilliant 50-22 set up another Springbok lineout five metres from the Italian line, it seemed inevitable they would score.
Captain Siya Kolisi duly crossed to secure the bonus point with only 23 minutes on the clock.
Number eight Jasper Wiese then broke clear after De Jager charged down a kick and passed inside to Damian Willemse, who crossed unopposed under the posts.
Italy's cause was not helped by a yellow card for prop Muhamed Hasa for a deliberate knock-on on the half-hour mark.
Marx crossed for his second try from another driving maul as the visitors took a remarkable 45-0 lead into the break.
South Africa were sloppy at the start of the second half with numerous handling errors, but when they did find their rhythm, they cut through Italy with ease as replacement prop Wilco Louw crossed for their seventh try.
The Boks continued to make errors as their second-half performance fell well short of the standards they had set in the opening 40 minutes.
Italy finally got on the scoreboard just past the hour mark when Federico Ruzza crossed in the corner.
Replacement Paul de Villiers scored from a driving maul to complete the rout, though a concern for the Springboks will be the players who left the field for head injury assessments, with potentially serious implications for next weekend's clash against France.
Ethan Hooker crossed for a late score to add the cherry on top for the visitors.
