Two half-centuries in the Derbyshire top order carried the visitors to 207-3 at the close, trailing Glamorgan by just 76 runs with seven wickets in hand at Swansea.
Ben Slater (52) and Alex Hughes (67 not out) both scored above 50 and there were useful contributions from Wayne Madsen (41) and Harvey Hosein (35) as Derbyshire responded well to Glamorgan’s 283 all out.
Earlier, Tony Palladino took his fifth of the match, his 12th five-wicket haul for Derbyshire, and Matt Critchley rounded off the Glamorgan innings with a run out after they added 108 to their overnight score.
Prem Sisodiya was dropped on 24 off Duanne Olivier early in the morning, but the debutante was out 14 runs later, bowled by Palladino as the seamer picked up his 398th first-class wicket.
Andrew Salter went on to make the top-score of the Glamorgan innings and reached his half-century in partnership with Lucas Carey (28).
Their stand was broken by Hamidullah Qadri, who had Carey caught by Billy Godleman to pick up his first wicket of the innings.
Michael Hogan was run out soon after to leave Salter unbeaten on 72 and Glamorgan all out for 283, a good response in improving batting conditions after being 53-5 at tea on Day One.
Leading the Derbyshire reply, Chesterfield-born duo, Slater and Hosein started well and surpassed their 50 partnership in the 19th over.
Slater reached his half-century off 97 balls, bringing the milestone up with his seventh four, but Hosein was out at the start of the next over, bowled by Salter for 35.
The off-break bowler then swung momentum back towards the hosts and had Slater out two overs later, caught by Sisodiya for 52.
Heading into the tea interval on 104-2, trailing by 179 runs and in need of another substantial partnership, Madsen and Hughes delivered with a stand of 84 as Derbyshire continued to chase down Glamorgan’s total.
Madsen was eventually out for 41, caught at mid-wicket off Jack Murphy, but Hughes pushed on with Billy Godleman and reached his half-century soon after.
With his first half-century in the Specsavers County Championship this summer, Hughes struck Murphy for back-to-back fours and brought the deficit below 100 as the visitors regained control after Glamorgan’s resistance in the morning.
Alongside Godleman (5 not out), Hughes looked assured for the remainder of the day as Derbyshire closed on 207-3 to pick up a bonus batting point, trailing Glamorgan by 76 runs.
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