Tony Palladino took 4-49 and there were two wickets for Ravi Rampaul, but lower-order resistance from Glamorgan saw them close on 175-7 after earlier being 53-5.
It was a good opening day for Derbyshire’s bowlers, as Palladino found movement off the surface in Swansea to rip through Glamorgan’s top-order.
Chris Cooke hit 69 and Andrew Salter closed unbeaten on 26 as the hosts fought back from being five down at tea to end Day One 25 runs short of a bonus point in a day edged by Derbyshire.
The start of play was delayed by a persistent drizzle at the St Helen’s Ground, Swansea, but groundstaff worked to get the outfield fit and play eventually got underway at 3.20pm.
Glamorgan won the toss and elected to bat first as openers Nick Selman and Jack Murphy were watchful in the middle.
But both fell to Palladino and Duanne Olivier in quick succession as Derbyshire took an early advantage before tea, the South Africa quick picking up his 27th of the first-class campaign.
The experienced Palladino soon had three in the opening session, Owen Morgan (4) caught behind and the dangerous Usman Khawaja bowled by an in-swinging delivery for 5.
The Derbyshire bowlers were dominant in the opening 21 overs and reduced the visitors to 53-5 at tea, with Rampaul picking up the fifth and Palladino heading into the interval with 3-13.
Glamorgan fought back after tea as Cooke struck Olivier for two fours and David Lloyd looked to attack Rampaul as the pair brought up their 50 partnership.
It was Rampaul who ended the stand on 58, Lloyd caught behind for 21, bringing Salter to the crease to join Cooke.
The pair set about rebuilding again, Salter watchful and Cooke continuing to find the ropes in his near run-a-ball innings. Glamorgan past 150 an onto 162 before the pick of the bowlers struck again, Palladino bowling Cooke for a well-made 69.
Salter saw out the rest of the day with debutante Prem Sisodiya and the hosts will resume on Day Two on 175-7.
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