Brown got to three figures with a six off Tim van der Gugten and immediately declared Sussex’s second innings on 263 for six, setting Glamorgan a target of 275 to win in 51 overs.
Off-spinner Jack Carson took three wickets and there were still ten overs remaining when Kiran Carlson top-edged a sweep to leave Glamorgan 131 for five, but Andrew Salter and Dan Douthwaite stood firm, taking their side to 154 for five when the players shook hands after two balls of the final over.
Stuart Meaker had removed opener David Lloyd for 17 in his fourth over with the new ball, courtesy of a smart catch at second slip by Aaron Thomason, and after tea Carson took his tally of Championship wickets to 31, making him Sussex’s leading-wicket taker in the competition.
Colin Ingram (27), Billy Root (12) and Carlson (23) all perished to catches by fielders clustered around the bat while opener Joe Cooke, who faced 89 balls for his 19, failed to pick Will Beer’s googly. But Salter, promoted from no.10, stood firm, absorbing 58 balls in his 19 not out.
Both sides took 12 points, meaning Sussex will finish either fifth or sixth while Glamorgan have the chance to end third if they can beat Northamptonshire in their next match starting on Sunday.
Brown had earlier extended his fifth wicket stand with Ali Orr to 100 before opener Orr’s impressive innings ended the ball after they had reached their milestone when he was leg before to David Lloyd’s inswinger for 80, made off 193 balls with ten fours. It was an excellent effort by the 19-year-old left-hander who has made half-centuries in his first two Championship innings.
Dan Ibrahim (17) was leg before hitting across the line at van der Gugten but Brown and Will Beer upped the tempo after lunch, adding 65 for the seventh wicket in 11.1 overs as the field spread and Glamorgan waited for the declaration.
Brown’s second hundred of the season came off 134 balls, the second 50 taking 53 deliveries. He hit six fours and deposited van der Gugten over mid-wicket before going to his century later in the same over. Glamorgan’s most successful bowler was van der Gugten, who finished with three for 44.