Kent 189 for 9 (Stevens 64, Stewart 60*, Fuller 3-47) lead Middlesex 161 (Stevens 4-44) by 28 runs
Denly and Gubbins, touted as possible tourists for England's winter trips to Sri Lanka and West Indies, both missed their cue under the watchful eye of selector James Taylor.
Instead it was 42-year-old Darren Stevens who starred with ball (4-44) then bat (64) for the visitors, while James Fuller 37 not out and 3 for 47 underlined his all-round value to the Lord's tenants. It all meant Kent closed 28 ahead with their last pair at the crease.
In the era of the uncontested toss, being stuck in on a sporty September pitch against the country's leading wicket-taker Matt Henry didn't look to bode well for a Middlesex team who'd gleaned just nine batting points from 11 games this season - and so it proved.
Henry made the initial incision aided by a poor shot from Gubbins (17) who swished one into the hands of Sean Dickson at first slip. Thereafter, it was the evergreen Stevens who took centre-stage, trapping Sam Robson lbw with his first delivery.
Middlesex's next wound was self-inflicted, Max Holden, promoted to No 3, throwing his wicket away setting off for a run which was never there, Henry running out the youngster with a direct hit from point.
Stevens was then at it again dismissing Dawid Malan and Eoin Morgan in quick succession and there was still time for former Middlesex quick Harry Podmore (3 for 35) to strike two further blows, Stevie Eskinazi and debutant Martin Andersson the men to fall, leaving the hosts 80 for 7 at lunch.
On the resumption Middlesex's tail found the resistance which had eluded their top order, Fuller sharing stands of 39 with Ollie Rayner (19) and 41 with last man Steven Finn (27) allowing them to scramble up to 161 all out.
Not for the first time this season Middlesex took the field with too few to defend and without leading wicket-takers, James Harris (groin) and Tim Murtagh (ill).
Ethan Bamber made an early breakthrough pinning Dickson in front and Steven Finn, back from injury, cut short Denly's chance to impress when he too had an LBW shout upheld.
Then it was Fuller's time to shine, the all-rounder emulating Stevens's feat from earlier in the day trapping Zak Crawley lbw.
Dander up the former Gloucestershire man then found the edge of Daniel Bell-Drummond's bat, wicketkeeper Eskinazi pulling off a stunning one-handed catch away to his right.
Skipper Sam Billings soon became Fuller's third victim and when Anderson scattered Heino Kuhn's stumps the visitors had crumbled to 53 for 6.
Again, though an interval came to the batting side's rescue as Stevens came out on the offensive producing a spate of boundaries as Middlesex bowled too short.
Podmore didn't last long playing a Finn long hop to Morgan at deep backward point, but Grant Stewart, who scored a maiden first-class century against Middlesex in the reverse fixture back in June, provided strong support.
The 50-stand was raised before Steven's ninth boundary via a top edge over the keeper took him to his half century in 62 balls. The fun ended at 64 when Anderson rearranged his furniture, but Stewart's third first-class 50 steered Kent to a precious lead.