Kent 82 for 4 trail Middlesex 147 (Stoneman 59, Stevens 4-21) by 65 runs
Darren Stevens took 4 for 21, including a spell of 3 for 3 from five overs, as Middlesex collapse from 121 for 2 to 147 all out at Canterbury before Kent closed on 82 for 4, trailing by 65.
Mark Stoneman top-scored with 59 but Stevens' efforts, with Matt Milnes claiming 2 for 31 and Nathan Gilchrist 2 for 34 in support, meant they slumped to a low total.
Tim Murtagh then took 2 for 19 as Kent navigated a perilous final session, Ollie Robinson and Milnes the not out batsmen at stumps on 11 and nought respectively.
Second hosted first in the final red-ball fixture of the season, with the winners guaranteed to finish top of Division Three. Kent won the toss, chose to bowl and entered the field to a standing ovation, following Saturday's triumph in the Vitality Blast at Edgbaston.
Sam Robson made 13 before he was caught behind off Gilchrist and Stevie Eskinazi was lbw to Stevens for 15, but Middlesex made it to lunch without further loss, ending the session on 84 for 2.
Stoneman brought up his fifty with a straight drive to Milnes that went for three, but Middlesex then lost five wickets for ten runs.
Stoneman chopped a Stevens delivery onto his stumps and Stevens then trapped Max Holden lbw for a six-ball duck, before Grant Stewart sent Martin Andersson's middle stump flying for nought. Stevens' fifth over of the session saw him get John Simpson caught behind for six and Luke Hollman went for golden duck when he was lbw to Marcus O'Riordan.
Toby Roland-Jones made nine when he chipped Milnes to a tumbling Stevens at mid-on and Ethan Bamber lasted just three balls before edging Gilchrist to Jack Leaning at third slip, without scoring. Murtagh then went for the fifth duck of the innings when Milnes yorked his leg stump to end the afternoon session.
Kent's reply got off to a rocky start when Jordan Cox left a ball from Murtagh that clipped his off stump, bowling him for two. Zak Crawley, captaining the side in the absence of Sam Billings - who is quarantining in UAE before he links up with Delhi Capitals - was caught behind off Bamber 20 and Daniel Bell Drummond was lbw for 20 to Murtagh. Leaning was then bowled by Anderson for 27, leaving Milnes to survive the two overs as night-watchman.