After a relatively quiet first half, Bolt came alive in the 57th minute when he showed his pace and strength to outmuscle a defender and buried a left foot strike past Eze Consoni.
The goal appeared to lift a weight off the Jamaican's shoulders as he bids to win a professional contract with the A-League outfit.
— Central Coast Mariners (@CCMariners) October 12, 2018
His second came 12 minutes later when he showed a striker's instinct and took advantage of a horrible mix-up between defender and goalkeeper to tap in from a couple of yards out.
All eyes were on the 32-year-old at the Campbelltown Stadium as he partnered captain and Aston Villa loanee Ross McCormack up front.
But Bolt appeared to be deprived of service for much of the first half – the Mariners preferring to play up the wings leaving Bolt with an outstretched arm in the air, similar to his trademark Lightning Bolt celebration.
The few attempts he had in the opening frame were fruitless: a scuffed shot finding the waiting arms of the keeper and a pacy run to connect with a probing cross falling wide.
The Mariners went into the break 2-0 up as Tommy Oar found McCormack for the opener on eight minutes and Jordan Murray scoring three minutes before the break.
But Bolt appeared more hungry after half-time and it paid off.
He brought out his trademark celebration after scoring his first Mariners goal, the striker being played in by McCormack on the left, shrugged off a United defender and fired in low beating Consoni at the near post.
The eight-time Olympic champion made way in the 75th minute with the game settled, applauding the fans as he made his way to the sidelines.
Bolt signed autographs on the touchline after he was taken off as the game fizzled out.