The Buccaneers bossed the midfield and had the lead just after the hour-mark when Teko Modise’s cross was met on the volley 30-yards out by Mhlongo, with the ball nestling in the top corner and leaving Swallows goalkeeper Greg Etafia with no chance.
The defeat leaves Swallows still looking for their first win of the season, while Pirates have two wins and a draw from their three matches.
There was also a first appearance in a Buccaneers shirt for Terror Fanteni, who came on as a substitute with 10 minutes remaining.
Pirates almost broke the deadlock in the opening seconds of the game, with their first movement from kick-off seeing Thulasizwe Mbuyane testing Etafia with a powerful shot.
Pirates stopper Moeneeb Josephs denied Lungisani Ndlela with a superb low save in a one-on-one situation in the 18th minute and he frustrated the tall striker again on 28 minutes, tipping a long-range effort over the crossbar.
However, Pirates were still able to create chances of their own. Modise fashioned a good opportunity for Katlego Mashego just past the half hour-mark, cutting inside from the left and clipping a good cross into the penalty area, but the striker’s acrobatic volley didn’t test Etafia.
But it took a piece of genuine class from Mhlongo to break the deadlock, with the midfielder getting on the end of Moside’s cross and striking a terrific dipping volley with the outside of his foot that rippled the back of the net.