Yorkshire 280 for 4 (Malan 145*, Tattersall 64*) v Derbyshire
Dawid Malan scored a superb unbeaten maiden Yorkshire century in challenging conditions as the hosts had much the better of day one against fellow Bob Willis Trophy challengers Derbyshire at Emerald Headingley.
Both sides have won their opening two North Group games, with Derby leading the race for top spot by four points.
However, the visitors, missing the experience of Luis Reece, Ravi Rampaul and Tony Palladino, were unable to capitalise on a couple of openings having won the toss and elected to bowl under slate grey skies.
Yorkshire fell to 40 for 2 and 106 for 4 either side of lunch before closing on 280 for 4 from 78 overs.
Malan finished on 145 not out from 180 balls and Jonny Tattersall unbeaten on 64 from 142. Bad light ended play early.
Fluent Malan's England team-mate Jonny Bairstow - this will be their last four-day group appearance if they win national limited-overs selection for series against Pakistan and Australia - made 22 having been dropped on nought.
The feature of Malan's knock was his dominant driving - both through the covers and down the ground. He shared a third-wicket partnership of 66 with Adam Lyth from mid-morning to early afternoon and then an unbroken fifth-wicket stand of 174 inside 44 overs with a quieter Tattersall.
This is the England left-hander's competitive home debut for the White Rose following his winter move from Middlesex. He hit a friendly half-century here against Durham last month before a match-clinching 73 came against the same opponents at Emirates Riverside in the opening round of this competition at the start of the month.
It was a helter-skelter start to proceedings under the Headingley floodlights - they remained on all day.
Ben Aitchison had Tom Kohler-Cadmore caught at third slip for a duck, off an under-edge as he tried to leave alone, leaving Yorkshire at 2 for 1 in the second over. In the third, Adam Lyth then pulled South African left-armer Michael Cohen for back-to-back sixes.
Bairstow was dropped on nought by Derby captain Billy Godleman at mid-off following an uppish drive at Dustin Melton. Bairstow went on to drive three boundaries - two particularly convincing either side of mid-off - and pull another before he pushed aggressively at seamer Anuj Dal and edged behind.
That left Yorkshire 40 for 2 in the 16th over, bringing Malan to the crease. He shared that 66 with Lyth until early afternoon before Cohen, particularly wayward at the start of the day, returned with more vigour to remove Lyth for 31 and Harry Brook for nought within the space of four balls.
From there, Derby would have hoped for more rewards, with conditions still beneficial. Swing and seam were apparent, while there was also evidence of a two-paced surface.
But in Malan they came across a batsman in serene touch as he set about his 26th first-class century. He reached his fifty off 87 balls and then his century off 136, by which time Yorkshire had gone beyond 200 for a first batting bonus point.
The century stand between Malan and Tattersall - playing as a specialist batsman with Bairstow taking the wicketkeeping gloves - had also been confirmed. Tattersall's innings was understated but a crucial foil for Malan, who later lofted Matt Critchley for six over long-off.
Tattersall worked the ball well on the way to a 122-ball fifty and will hope to convert to a maiden first-class century against county opposition.