The Brazilian forward was named on the bench by Pep Guardiola and after coming on with 20 minutes left he made his mark in the 81st minute, rifling into the roof of the net from a tight angle from Kevin De Bruyne's pass to put City 2-0 up.
It was a superb predatory finish from the 23-year-old and after the game, Jesus made it clear that he was delighted to be back after his spell on the sidelines.
"It’s so good for me to be back," Gabriel said. "When I got injured, I wasn’t happy, I worked a lot to recover quickly because I want to be on the pitch and helping my teammates.
"The guys have done so well and I’m so happy to come back and score a goal. It was a good ball and a great play by the team. Kevin found me and I think it was an amazing finish.
"I made it hard for the keeper and I’m getting better at my finishing."
Guardiola's men went ahead early through Ferran Torres, but found it challenging to break through the rigid Olympiakos backline before Jesus gave us some breathing space with nine minutes to go.
Fellow sub Joao Cancelo added a superb third in stoppage time, but Jesus admitted that he was plotting to breach the Greek side's rearguard from his seat on the bench.
"I think games like these are difficult," he continued. "From the bench, I watched closely how the opposition defenders were playing so when I got on the pitch, I got the one chance and took it."