Singh kickstarted the day by claiming Tommy Boorman lbw with a delivery which straightened and dismissed Miles Hammond in his next over for a duck, but in contentious circumstances.
What was appealed for as a caught and bowled was, after the umpires conferred, given – to the bemusement of Hammond who took his time to trudge off.
A substantial middle order collapse followed, for which Singh was primarily responsible and superbly supported by Matthew Waite, wo took 3-14 from 16 overs and deservedly opened his own account when pinning James Bracey lbw without offering a shot.
Waite then removed stubborn Cameron Bancroft for 56 from 145 balls, who intended to push an inswinger into the off-side but only succeeding in picking out Ben Allison at square leg.
By this stage, Gloucestershire were in real trouble and still behind in the game at 97-5, and Worcestershire struck further blows to extend the collapse.
Jack Taylor, injured in the first innings, limped to the crease but he was clean bowled by Singh with a beauty which pitched on middle before beating the bat and clipping the top of off-stump.
And he had a fourth before lunch with another caught and bowled, when Kristian Clarke popped up a leading edge.
Van Buuren (32 from 50 balls) and Daaryoush Ahmed repelled Worcestershire’s attack immediately after lunch and shared in a stand worth 50 runs for the eighth wicket, before Waite sent the former’s off-stump flying.
When Ahmed (27) also perished, becoming Singh’s fifth victim after edging to Ethan Brookes at first slip, the end of Gloucestershire’s modest innings was in sight.
Tail enders Will Williams and Luke Charlesworth did drag matters out, but the new ball did the trick when Beyers Swanepoel – with the first delivery of his spell – trapped Williams with a full ball which proved too good.
That left Worcestershire with what appeared a relatively straightforward task with the bat, but Van Buuren instantly got turn and removed Dan Lategan in the very first over of the pursuit to set a few pulses racing.
Worcestershire promoted Swanepoel up to three following the early dismissal and he put a dent in the target with 35 off 38 balls.
The wily Van Buuren was relentless from one end, however and he removed Jake Libby and then Swanepoel, who was caught at short leg to make it 52-3.
When Adam Hose pushed Clarke to Bancroft, Worcestershire were still 30 runs short and seemingly making a meal of securing their humble target.
Captain Brett D’Oliveira was the next to depart when he nicked van Buuren into Bracey’s gloves, but Brookes and the steady Gareth Roderick (24 not out) guided Worcestershire through the remainder of what proved to be an awkward chase.
Report by ECB Reporters’ Network, supported by Rothesay.
Worcestershire head coach Alan Richardson:
“It was fairly nerve-wracking towards the end. It’s another game that has gone to the wire.
“The wicket was tricky to score on, but both sides showed that occupancy of the crease was possible as well. Hopefully it was an intriguing game for those who watched it.
“Throughout the game I thought we bowled really well, especially as a seam group. We kept a lot of pressure on. The wicket favoured bowlers at times, but we had to be patient.
“We had a window of opportunity and I felt like we took the chance to win the game. It was pleasing, it was nice for those who worked so hard in the first innings to get their reward in the second.”
Gloucestershire head coach Mark Alleyne:
“We came into this game on the back of a really bad run for the whole Championship. We were hopeful coming here, having won the toss, that we could get a good score in the first innings.
“I think 280 was a fair effort but definitely below par having had first usage, I think 350 would have been better, to help us put more pressure on their first innings.
“Winning the toss and batting first we thought was a significant advantage to have, we expected the pitch to deteriorate quite badly and it did offer excessive turn.
“The spinners dominated. It was quite a good four-day cricket pitch, but there was intrigue and jeopardy – good to watch if you’re a neutral.”
BBC News