The Australian Di Venuto rattled off 162 runs at Hove as Chris Adams' men successfully chased Gloucestershire's 452-run challenge. It was a club record total for batting fourth.
At the start of play Sussex still needed 325 and Di Venuto reached his 100 in 203 minutes off 165 balls. Aided by Cottey, who crafted a gutsy 126 and shared a fourth-wicket stand of 256 in 73 overs with Di Venuto Sussex were able to meet the improbable target.
Hampshire went top of the Championship table with a hard-earned six-wicket victory after a day of determined and dogged batting at Lord's. Mike Roseberry's 116 took Middlesex to 339 which left Hampshire needing 217 for victory.
They won with 15 balls to spare as an unbeaten 78 from Will Kendall and 64 from Giles White.
In another thrilling finish against long odds Graham Lloyd and Glen Chapple took Lancashire to a first Championship win of the season against Nottinghamshire at Old Trafford.
They hammered 99 runs from 21 overs for the seventh wicket to take Lancashire within three of a tough victory target of 332.
Chapple was out for 55 but Lloyd completed Lancashire's three-wicket win, ending unbeaten on 120 for his first century of the season.
Ian Fisher spun Yorkshire to a comfortable 173-run victory over a disappointing Essex at Chelmsford. The 23-year-old left-armer emerged with career-best figures of 5 for 73 as the home side were bowled out for 237 despite Stuart Law following up his first-innings 159 with an unbeaten 113.
At Edgbaston Warwickshire beat Worcestershire by 51 runs despite a valiant rearguard action by the visitors.
Worcestershire made a game of it with Chris Liptrot's 61 and Paul Pollard's 58 but Graeme Welch spearheaded a nerve-jangling finale.
After Worcestershire had defied Warwickshire for most of the day, Welch took the new ball with less than 25 minutes remaining.
Tim Munton dismissed Phil Newport and Welch clinched victory by taking the last wicket of Alamgir Sheriyar with just nine minutes to spare.Reuse content