Ravi Rampaul claimed his tenth first-class five-wicket haul, but Glamorgan fought back well on another closely-matched day of cricket at The Pattonair County Ground.
He took 5-94 as Derbyshire dismissed the visitors for 346, with Charlie Hemphrey top-scoring with 75, to earn a 32-run first innings lead.
Resuming in the afternoon session, Wayne Madsen’s 47 helped the hosts to a lead of 203, but four wickets for Dan Douthwaite (4-33) sets up a finely-poised Day Four.
Glamorgan resumed their innings on 214-4, with Billy Root, unbeaten on 53, and Jeremy Lawlor at the crease.
After a bright start to the day from Rampaul, Lawlor almost fell when a nick off the outside edge was put down by Alex Hughes while on six. The drop proved inconsequential, as Rampaul trapped him lbw for 10 two balls later.
Derbyshire continued their strong start to Day Three with the wicket of Billy Root in the 78th over. Luis Reece was the bowler to claim the lbw, with Root falling for 68 from 93 deliveries.
From there, Derbyshire were frustrated by the new partnership of Tom Cullen and Douthwaite, who put on a half-century stand and went into lunch on 299-6.
Rampaul broke the partnership after lunch, finding Douthwaite’s (39) outside edge with a ball that carried to Harvey Hosein behind the stumps.
He claimed his fourth wicket two overs later, dismissing Cullen with a delivery which uprooted the off-stump, leaving Glamorgan 318-8.
Reece (3-53) got in on the act to claim the wicket of Andrew Salter without scoring, finding the outside edge and caught by Hughes in the cordon.
Rampaul (5-94) completed his five-wicket haul by having Lukas Carey (24) caught in the deep by Tom Lace. Glamorgan finished on 346, trailing Derbyshire by 32.
Reece and Billy Godleman opened the innings for Derbyshire, with the latter falling in the sixth over, caught behind for nine off the bowling of Michael Hogan.
Reece and Wayne Madsen put on 48 before tea, with Madsen striking 32 from his first 30 balls.
Madsen fell in the 26th over for a score of 47 when he was caught by Selman off the bowling of David Lloyd. Along with Reece, the pair put on 80 runs for the second wicket.
Reece departed two overs later after being caught by Selman off Lloyd for 31, having guided Derbyshire to 112-3, while Harvey Hosein managed four before being caught down the leg side by Cullen while trying to hook Douthwaite.
Lace eventually departed for 29 after he was bowled by Douthwaite. He had remained at the crease for 44 balls. Later in the same over, Matt Critchley was out lbw for 11.
With Dal (6 not out) and Rampaul (8 not out) at the crease, Derbyshire head into Day Four on 171-9, leading by 203.
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