Nottinghamshire 324 (Hameed 68, Patel 63, Nash 59) and 84 for 3 (Hameed 30*, Mullaney 27*) lead Derbyshire 239 (du Plooy 130) by 169 runs
A century from Leus du Plooy has left the Bob Willis Trophy match between Derbyshire and Nottinghamshire in the balance after two days at Trent Bridge.
The South African left-hander scored 130, which included 17 fours and three sixes, off 177 balls and shared a 10th-wicket stand of 80 with Sam Connors, a Derbyshire record against Nottinghamshire.
It lifted his team to 239, 85 runs behind, and Connors then took 3 for 19 in eight overs before Nottinghamshire recovered to 84 for 3 , a lead of 169, with the North Group game intriguingly poised.
There were times when Nottinghamshire threatened to take complete control only for a combination of superb batting and indifferent bowling to turn the contest.
Jake Ball swept aside Derbyshire's top order in a fine opening spell only for du Plooy and Matt Critchley to regroup before a post-lunch collapse saw Nottinghamshire regain the initiative.
At 159 for 9, Derbyshire were on the ropes but Connors played resolutely while du Plooy ruthlessly put away the bad balls of which there were too many as Notts persisted with short-pitch bowling.
Even Ball, so relentless in his line at the start of the day, lost control as du Plooy lofted him over long-on to reach his century and later pulled and drove him for two more sixes.
The pair passed Derbyshire's previous 10th wicket record against their neighbours of 74 at Ilkeston in 1969, increasing Nottinghamshire's frustration with every delivery, when du Plooy tried to hit Samit Patel over the top and Joey Evison ran back from mid off to hold a diving catch.
Under normal circumstances, du Plooy would have walked off to a standing ovation but the applause of all the Notts players acknowledged the quality of his innings.
They would have expected to be batting again long before tea when first Ball removed Luis Reece, Billy Godleman and Wayne Madsen in four overs from the Radcliffe Road End and then six wickets fell for 40 runs in the afternoon.
A farcical run out first ball after lunch started the slide with Critchley stranded at his partner's end although it needed a smart reaction from Steven Mullaney to break the stumps after a wretched throw from midwicket threatened to reprieve the batsman.
Evison had Harvey Hosein and Fynn Hudson-Prentice lbw in quick succession before Mattie McKiernan was smartly caught at gully and it looked as if du Plooy would be stranded when Tom Barber removed Michael Cohen and Ben Aitchison to claim his maiden first-class wickets.
But Connors stood firm as du Plooy combined orthodox strokes with one-day improvisation to score 69 in 19 overs and the momentum remained with Derbyshire in the evening session.
Chris Nash and Haseeb Hameed shared a century opening stand on the first day but when Nash tried to pull the second ball from Connors, he got a bottom-edge into his stumps.
Ben Duckett looked in good touch until he tried to turn Connors off his hip and was caught behind down the leg side and in the fast bowler's next over, Joe Clarke walked across and was lbw although his reaction suggested he thought the ball was missing leg stump.
Another wicket would have really set nerves jangling in the Notts dressing room but Haseeb Hameed and Mullaney played calmly through the remaining 14 overs.