David Ripley's side were defeated by 34 runs at the County Ground as they failed to get close to chasing down the Foxes 200 for two.
Josh Inglis struck a T20 career-best 103 not out for Leicestershire as they got their campaign up and running at the sixth time of asking.
But it was more misery for the Steelbacks, who have now lost five of their six matches, with the other game a wash-out at Worcestershire Rapids on Friday night.
Yorkshire-born Australian Inglis thrashed four sixes and 13 fours in a stunning 62-ball knock, sharing a century stand with skipper Colin Ackermann for the third wicket.
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Callum Parkinson then took two for 19 and Gavin Griffiths two for 23 to make sure the Steelbacks fell well short, finishing on 166 for seven despite an unbeaten 50 from Rob Keogh.
After Leicestershire won the toss and opted to bat, Inglis dominated from the off, his six over mid-wicket off Ben Sanderson in the second over a sign of things to come.
Fellow opener Scott Steel left early after splicing Tom Taylor to mid-off, and the hosts were left to regret skipper Adam Rossington missing a chance to stump new batsman Arron Lilley when he had made just 12, Mohammad Nabi the unlucky bowler.
Lilley made the most of the reprieve, hitting Graeme White for successive sixes, the second landing in a garden of nearby Clark Road, as he made 44 off 29 balls in a second-wicket stand of 67 with Inglis before holing out at mid-off.
Inglis, starved of strike during that stand, picked up where he’d left off, going to 50 off with a glorious straight six off White.
With Ackermann (31) content to play second fiddle, Inglis unfurled nine more fours, finding all parts of the boundary in a stellar display of improvisation.
He would also outdo team-mate Lilley in smiting the biggest six of the day before dinking Sanderson over fine leg to reach three figures in the final over.
The Steelbacks were then struck by an early blow in reply as Rossington sliced one skywards to backward point off the bowling of Parkinson.
Richard Levi responded by bludgeoning Ackermann over the ropes at cow corner, but the visitors struck again when Naveen-ul-Haq produced a brute of a Yorker which struck Ricardo Vasconcelos on the foot, leaving him plumb LBW.
Levi (30) was castled by a flighted delivery from Ackermann before Griffiths struck twice in three balls, removing Wayne Parnell for 15 and Saif Zaib for a duck to leave the hosts 69 for five.
Nabi hit a six onto the pavilion roof and Keogh reached his half-century from the last ball of the match, but the game was long gone.