Rob Key had hit only 61 this summer in five previous Championship knocks
Kent became the first team in history to boast four centurions in a County Championship innings as they enjoyed a run spree against Surrey at The Oval.
Kent captain Rob Key (123) joined forces with Joe Denly, who also hit 123, in a first-wicket stand worth 247,
Martin van Jaarsveld (110) and Justin Kemp (121no) then piled on the agony with another double-century stand of 214 in 56 overs.
By the close, replying to Surrey's 386, Kent had posted 509-5.
The likelihood is that Key will declare overnight and bid to bowl the dispirited Brown Caps out cheaply in order to secure the win that would take them top of Division Two.
In between the two double century stands, ironically, there was a Kent collapse in which they lost four wickets in 28 balls.
Resuming on their overnight 152-0, Kent pushed on at a lusty pace as Denly hit two sixes and 12 fours to reach his third hundred this summer.
Key, by contrast, was posting three figures for the first time this season in Championship cricket, more than doubling his previous output of just 61 in three matches.
And he flamboyantly made light of the supposedly nervous 90s with 13 off one Murtaza Hussain over, including a straight six, a paddled four and a cover-driven two.
Kent's run glut ended in the run-up to lunch when Surrey strutted for the one and only time during the day.
Denly was run out by substitute fielder Laurie Evans after answering Key's call for a questionable single to square-leg. Then Geraint Jones and Darren Stevens both chalked up ducks.
To add to Kent's temporary malaise, Key was involved in a second run-out when Hussain tipped a firm drive by Van Jaarsveld back onto the stumps at the non-striker's end to catch Key out of his ground backing up.
Kemp and Van Jaarsveld then claimed centre stage until just after the scheduled six o'clock finish time when, in time added on for two short bad-light stoppages, the latter fell leg before when trying to on-drive Alex Tudor.
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