Italian Jacobs, who stunned the athletics world three years ago with two golds in the Covid-delayed Tokyo Games, clocked a time of 10.07 seconds to win his race at the 'Sprint Festival' in Rome.
The 29-year-old finished 0.04sec ahead of Chituru Ali in a race against five of his countrymen at the low-key event, starting sluggishly before eventually surging through to win.
"The race was OK, I'm having these errors at the start which are making me slower than I know I can be," said Jacobs to Sky.
"If I'd managed to get my start going as I had during the warm-up it would have been a different race because the start is the basis from which you can reach your top speed.
"I was missing that, but I'm very happy with the second part of the race."
Saturday's win kicked off a run of competitions for Jacobs, who said he was suffering from hay fever, before the Olympics begin on July 26, after returning to Italy from his new base in Florida.
Next Jacobs will compete in Ostrava on May 28 and the Oslo Diamond League event two days later, ahead of defending his European 100m title in Rome next month and then his 100m and 4x100m relay Olympic crowns in Paris.
Jacobs, also a former 60m indoor world champion, has struggled with a series of muscular problems and flopped at last year's worlds in Budapest where he was eliminated in the semi-finals.
He has since teamed up with coach Rana Reider, whose Florida training group also includes American Trayvon Bromell, Olympic 200m champion Andre De Grasse and Japanese sprinter Abdul Hakim Sani Brown.
Jacobs came second over 100m to two-time world bronze medallist Bromell in an opening run-out in Jacksonville last month.
