O’Riordan, the 22-year-old off-spinner making only his third first-class appearance, took career-best figures of three for 50 and former Middlesex seamer Podmore bagged three for 74 while Brown stood firm for over four hours to see Sussex in at stumps on 320/9.
The visitors lost three wickets in the opening session all due to batting errors. After hitting four boundaries in a run-a-ball cameo worth 19, Phil Salt feathered a tentative prod outside off to the keeper from a Stevens leg-cutter to make it 27/1.
Second-wicket partners Harry Finch and Tom Haines added 50 from 80 balls before Kent debutant Tim Groenewald, bowling around the wicket, had left-handed Haines caught off an edged drive by Jordan Cox at slip for an attractive 21.
Then, on the cusp of lunch, Finch fell for 37, caught at slip when aiming to slog-sweep off-spinner Marcus O’Riordan.
Resuming after tea on 93/3, Sussex ploughed on through Ben Brown and Tom Clark who added 83 in almost 22 overs to take Sussex to their first batting bonus point. Clark contributed a 77-ball half-century - his first in the first-class game - with eight boundaries but the left-hander tossed away his wicket for 65 when dancing down the pitch to O’Riordan only to chip a simple catch to mid-on.
Sporting his new-look bleached grey hairstyle, Podmore, the former Middlesex seamer, then found the inside edge of Delray Rawlins’ bat with a booming in-swinger that flew to the keeper, and Robinson claimed his third catch of the day when Garton, on four and in the tea over, followed a Podmore leg-cutter to give Kent their second bowling bonus point.
Though conditions for cricket were ideal, the eery lack of crowd noise made for a strange start to Kent's opening first-class home fixture for 2020.
While Sussex changed in the Leslie Ames Stand hospitality boxes on the Nackington Road side of the ground, Kent used both dressing rooms on the pavilion side with a seven-player restriction per dressing room. As well as taking standard drinks intervals the players, who are unable to shower come each day’s end, also took short hand sanitisation breaks every 20 minutes.
In the final session Brown, the Sussex skipper, notched his side’s second half-century of the day from 101 balls and with six fours. Yet Podmore continued his good work by having Jack Carson held at second slip on the drive after the right-hander edged a floating away swinger.
O’Riordan mopped up his third wicket of the day when Henry Crocombe walked across his stumps working to leg to fall lbw then Stuart Meaker risked a second to deep cover only to be run out by Hamidullah Qadri’s throw from the ropes.
Clark said: “It feels great to get that first half-century out of the way and it was really nice to make a significant contribution to the team’s total.
“We spoke as a batting group about making sure we could get 300-plus batting first. In these games we have to make sure we can get into dominant positions to try and win games. It was pleasing to post this score today and for me personally to make a decent contribution. It’s massive for me to know I’ll get a decent run in the side throughout this Bob Willis Trophy.
”O’Riordan was turning the ball steadily and that’s encouraging for us, as we’re bowling in the fourth innings. We have a couple of really good spinners in our side and I believe that will only reinforce our decent position in the match after the opening day.”