Akani Simbine, from South Africa, claimed third in 10.02 seconds in a photo-finish with Britain's Chijindu Ujah.
"It was good," Bolt said of his 53rd sub-10 second 100 metres. "I'm going in the right direction, although there is still a lot of work to do. Sub-10 is always good."
Bolt has struggled to produce his best form this season, running 10.03 seconds in Kingston in Jamaica and 10.06 seconds in Ostrava in the Czech Republic in his only two outings this season. Both times are well behind the American Christian Coleman's world-leading 9.82 seconds which he recorded in Oregon last month.
Bolt’s victory in Monaco was far off his world record of 9.58 seconds which was set at the Berlin world championships in 2009.
That mark came a year after he had fulfilled his promise as a junior by exploding onto the senior circuit with gold medals in the 100 and 200 metres at the Beijing Olympics in 2008.
Four years later in London, the Jamaican became the first man to defend both Olympic sprint titles. He promptly declared himself a living legend on the back of the feat.
In Rio in 2016, he enhanced the myth with another successful defence of both crowns.
In all there have been eight Olympic gold medals and 11 gold medals at world championships in South Korea, Moscow and Beijing. At the London edition of the event in August, Bolt will try to add to his tally before he retires from competitive action.
"There are always mixed emotions,” said Bolt after the race in Monaco before a sell-out 17,000 crowd at the Stade Louis II. “I'm happy for my career but sad that it is ending."