Impressive Kirby launches Gloucestershire fightback
Kent established a first-innings advantage of 65 when they bowled Gloucestershire CCC out for 166 shortly after lunch.
But the hosts were reduced to 149-6 at stumps – and an overall lead of 214 – after Kirby took 4-25 in two impassioned stints from the Crystal Palace End.
Earlier Simon Cook, playing his third Championship match of the summer for Kent, returned season's-best figures of 5-22 to help the hosts take Gloucestershire's last eight wickets for 97.
Batting again by 2.30pm, Kent's top order also struggled to cope with the bounce of this sun-baked Worsley Bridge Road pitch and the pace generated by Kirby.
Again, it was first-innings top scorer Martin van Jaarsveld who showed the way with a second half-century in the game from 108 balls and with eight fours.
The tall South African, the only player to post 50 in this game to date, continues to weld together a fragile Kent side who persist in frustrating their membership by batting only slightly better second time around.
Openers Rob Key (12) and Sam Northeast (30) both fell to Kirby either side of tea.
Key was caught on the crease by an off-cutter then Northeast, who has been called up for the England Under-19 Test and ODI series against Bangladesh, starting next week, went leg before to a painful yorker on the left boot.
Kirby also chipped in with the scalp of Geraint Jones (4), who wafted outside off stump to edge to second slip, while Darren Stevens (3) nicked to the keeper as he push-drove at a lifting, turning ball from Vikram Banerjee.
Frustratingly for Gloucestershire, van Jaarsveld (62) teamed up with fellow South African Justin Kemp (25no) to add a useful 55 in 19 overs for the fifth wicket before van Jaarsveld's top-edged pull flew to the keeper to give Kirby a fourth wicket.
The start of the day had belonged to Cook. The tall, willowy former Middlesex seamer bowled the perfect length for this bone-hard pitch to run through the league leaders' middle order with his seventh five-wicket haul for Kent.
Resuming on their overnight total of 69-2 and in pursuit of Kent's seemingly below-par 231, Gloucestershire lost early wickets to spin before succumbing to Cook's seam.
Off-spinner James Tredwell enticed Alex Gidman (28) and Kadeer Ali (27) down the pitch to have them caught at mid-off and silly point, respectively, before Cook got in on the act by having left-hander James Franklin (7) pouched at slip – the first of four off Cook that flew to the keeper and slip cordon.
Stephen Snell (0) wafted across the line to go leg before then, soon after lunch, top scorer Craig Spearman (47) nibbled one to second slip to make it 151 one for seven.
Gloucestershire then lost their last three wickets for 11 runs.
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