Sussex need eight wickets on the final day to secure their first away Championship win of the season.
They had hosts Gloucestershire, chasing 276 to win, struggling on 30-2 at close of the third day at Cheltenham.
Having top-scored with 76 in his side’s first innings, Sussex batsman Harry Finch faced 143 balls, hitting 16 fours and a six, to score 98 as the backbone of a second innings score of 296 all out on a seamer-friendly pitch.
Luke Wright (48) and David Wiese (40) batted positively, while David Payne’s figures of 4-69 included his 200th first class wicket.
By the close, Gloucestershire had lost openers Chris Dent and Miles Hammond to Archer, and an enthralling contest will enter its final day with Sussex favourites.
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