Yorkshire 128 for 2 (Lees 61*) beat Derbyshire 127 for 6 (Madsen 34*, Rashid 2-19) by eight wickets
Australia star Aaron Finch was upstaged on his Yorkshire debut by local boy Alex Lees, who clubbed a superb unbeaten 61 in an eight-wicket win over Derbyshire.
The world's No.1-ranked Twenty20 batsman made his much-heralded arrival at Headingley after a spell in the Indian Premier League with Hyderabad, but scored just 19 as 21-year-old Lees stole the show and guided Yorkshire to their first NatWestT20 Blast win of the season.
Liam Plunkett and Adil Rashid took two wickets apiece as Yorkshire survived some poor catching to limit their visitors, who are still searching for a first win of the season in any format, to 127 for 6.
Derbyshire got off to a flying start and were 28 without loss after the first three overs before Stephen Moore became the first man to fall with Oliver Robinson, on Twenty20 debut, running him out with a direct hit from cover for 18. Robinson's debut got even better shortly after when he caught the dangerous Chesney Hughes at deep square leg as he attempted to pull Plunkett.
Derbyshire were rocking in the eighth over courtesy of two wickets in three balls from Rashid, who first bowled Marcus North round his legs and then had Wes Durston trapped lbw.
The clatter of wickets slowed the rate, with just two boundaries in the next five overs, before Plunkett claimed his second wicket, with Lees claiming Scott Elstone, who had earlier been dropped by Jack Leaning, at short-midwicket for 14.
Gareth Cross made 20 before he was done by Richard Pyrah's yorker and Wayne Madsen finished unbeaten on 34 as the visitors posted a seemingly below-par total.
Finch made a statement of intent with a six in the first over, but was then kept largely off-strike, briefly by Andrew Gale, who was caught at point by Elstone off the bowling of Mark Footitt for 7, and then by Lees.
In fact, Finch faced just nine balls in the first six overs as Lees took charge, hitting six fours in seven deliveries as Yorkshire powered to 70 for 1.
Finch fell for 19 when he was caught and bowled by countryman North, but Lees brought up his maiden Twenty20 50 off 30 balls in the next over. He and Jonny Bairstow, with an unbeaten 29 not out then guided Yorkshire home with 36 balls to spare and the minimum of fuss.