Tim Groenewald blew away the Somerset tail to give Derbyshire the lead after a rain-affected third day at the County Ground.
Groenewald, who had to play second fiddle to new ball partner Tony Palladino on Day 2, took the leading role on Day 3 dislodging three Somerset batsman to pick up his first five-fer of the campaign - ending with impressive figures of 5 for 30 from 18 overs.
Not to miss out, Palladino claimed the final wicket of the day to complete a five-wicket haul of his own, as the hosts wasted little time in dismissing the visitors for 216, sealing a 50-run lead.
Bad light, however, forced an early closure to proceedings with Karl Krikken's side on 36-2 - a lead of 86 runs - to leave the match finely poised with one day remaining.
Palladino destroyed the Somerset middle-order on the second day, picking up four wickets, as the visitors resumed the penultimate day on 180-6 in reply to Derbyshire's 266 all out.
When play finally got underway at 3.45pm, it took only four balls for Marcus Trescothick's side to lose their first wicket as Craig Meschede nicked Groenewald through to Richard Johnson for one.
Peter Trego and Alfonso Thomas provided some late resistance adding 29 runs for the eighth wicket, but the South African-born paceman made short work of the Somerset tail, clean bowling Trego (28) before removing Kirby (0) to end the innings with five wickets.
Palladino (5-97) removed Overton in the following over to also end with five, as Derbyshire secured a 50-run first-innings lead - claiming the last four wickets for just 36 runs.
With 28 overs remaining in the day, the hosts made a quick start in an attempt to set Somerset a final-day total to chase. But any hopes of setting a competitive score were dashed when bad light stopped play after just 10 overs. Derbyshire closed the day on 36-2, with Billy Godleman unbeaten on 19 and Shivnarine Chanderpaul yet to score.
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