Surrey bounced back from their last-gasp opening-night defeat to overcome Somerset by 14 runs at Taunton in the NatWest T20 Blast.
Jason Roy belted his second half-century in as many games to start the season to be the mainstay of Surrey's 173 for seven.
But this time Dernbach was able to celebrate in trademark style at the end as he completed the job with a final over that cost just three runs, in returning figures of 1-26 from four overs.
Craig Kieswetter’s aggressive 61 at the top of the order had seemingly set Somerset on target, but he fell during a wobble of three wickets for 13 runs that derailed the hosts as they finished on 159 for six.
Roy and opening partner Graeme Smith put on 29 in 23 balls before the former South Africa skipper was caught by countryman Alviro Petersen off Lewis Gregory for 20.
The six-over powerplay yielded 57 runs and Surrey advanced to 95 before the expensive George Dockrell had Steven Davies caught in the deep by James Hildreth for 24.
Three figures in the 11th over and Roy reached a 33-ball half-century featuring four fours and three sixes.
It appeared Surrey were set for a score in excess of 200 at that stage only for the clamps to be put on.
Gary Wilson became his Ireland team-mate Dockrell's second victim, the spinner's figures of 2-36 representing a good comeback after 23 came from his first seven balls.
Another Irishman, Kevin O'Brien, made just three and when Alfonso Thomas took the crucial wicket of Roy, well caught at mid-off by a diving Max Waller, the momentum was shifting.
Robin Peterson also went for three but Azhar Mahmood lifted Surrey with 27 off 15 balls before being run out off the last ball.
In reply, Marcus Trescothick was run out for eight following an early mix-up with Kieswetter – Dernbach picking up in his follow-through before turning and hitting the stumps at the non-striker’s end.
Peter Trego then skied a catch to third man, but Kieswetter scorched his way to a 31-ball half-century.
The wicketkeeper-batsman hit a four and a six as 14 came off the second over, bowled by Mahmood, and took two boundaries off Tom Curran in a fourth over also featuring five wides off a dreadful leg-side delivery.
His seventh four, off O'Brien, took him to 48 before a succession of singles completed his half-century.
Petersen had proved an able ally but, having made 23 from 17 balls, he lofted Zafar Ansari to Aneesh Kapil at deep cover.
And key man Kieswetter went for one big shot too many, heaving Ansari high into the Taunton skies but straight down the throat of O'Brien, who celebrated exuberantly.
Nick Compton followed for 12 off the first ball of the next over as Somerset’s wobble set in.
While Thomas improvised his way to an unbeaten 19 from 12 balls, Somerset came up short as Dernbach this time held his nerve.