Derbyshire 94 for 1 (Reece 50*) trail Sussex 100 (Chappell 4-32, Conners 4-39) by six runs
Only three players made double figures in a flimsy Sussex batting display after Derbyshire took full advantage of winning the toss.
After several days under the covers, the pitch offered some assistance although it was an undistinguished performance by Sussex whose promotion hopes were slim at best even before this collapse.
The tone was set in the fifth over by Ali Orr who aimed a big drive at Chappell without moving his feet and gave Guest his first victim.
Tom Alsop, leading the side in place of the suspended Cheteshwar Pujara, was also guilty of a loose drive at Conners three overs later and when James Coles threw his bat at a wide ball from Anuj Dal, Sussex were 40 for 3.
Tom Clark pulled a short ball from Pat Brown for six but when Dal found some late movement to have him caught behind, the innings went into freefall.
Dan Ibrahim was drawn into playing at a ball that left him to give Guest his fifth catch, the first time a Derbyshire wicketkeeper had achieved the feat before lunch since Bernie Maher on Royal Wedding Day in July 1981.
Oli Carter was cleaned up playing back to a full-length ball from Conners and after Chappell struck twice in successive overs, Sussex went into lunch on 77 for 8.
Only three overs were bowled after the interval before heavy rain delayed the game until 4.30pm but the second ball after the restart, Wayne Madsen damaged a finger trying to take a catch at second slip and left the field in obvious distress.
Former Derbyshire allrounder Fynn Hudson-Prentice took Sussex to three figures before Jaydev Unadkat pulled Conners to midwicket, and the innings ended in the next over. Hudson-Prentice skied a pull at Chappell to give Guest his seventh catch, which equalled the record set by former England great Bob Taylor in 1966 who then matched it in 1975 before Harvey Hosein achieved the feat in 2014.
It was the first time this season a wicketkeeper has completed seven dismissals in an innings in first-class cricket and his assured glovework consigned Sussex to the lowest total by a visiting team at Derby for 25 years.
The Sussex bowlers failed to match the consistent lines of Derbyshire’s attack which allowed Reece and Harry Came to add 65 in 18 overs before Came miscued a pull at Sean Hunt to midwicket.
That brought Guest back out to the middle and at stumps he had helped Reece take Derbyshire to within six runs of Sussex’s meagre total.