Gloucestershire 184 for 4 (Marshall 90, Shahzad 3-26) beat Sussex 173 for 9 (Wright 71, Taylor 3-29) by 11 runs
Hamish Marshall hit a 55-ball 90 to set Gloucestershire on their way to an 11-run victory over Sussex in the NatWest T20 Blast at Arundel Castle.
The Kiwi put on 120 with Ian Cockbain for the second wicket and a late cameo from Benny Howell saw Gloucestershire reach 184 for 4 from their 20 overs.
Matt Machan blasted an 18-ball 31 to give the 6,000-plus crowd something to cheer as the Sharks finished on 173 for 9, Matt Taylor taking 3 for 29.
The result lifts Gloucestershire to second in the South Group while Sussex remain in fourth place.
Gloucestershire got off to a slow start after being put in to bat and losing influential skipper Michael Klinger in the second over when the Australian was trapped lbw by Shahzad for 2.
The visitors were 28 for 1 after the opening five overs but then Marshall and Cockbain began to up the tempo.
The pair put on 120 in 75 balls with Marshall bringing up his 50 from 31 balls with six fours and a big six off leg-spinner Will Beer over midwicket.
Cockbain made 37 from 33 balls - including sixes off Danny Briggs and Twenty20 debutant George Garton - before being caught off a leading edge to give Briggs a solitary success.
Marshall followed for an excellent 90 when he cut Shahzad straight to Machan at point but the Gloucestershire innings did not lose any momentum after his departure.
Howell blasted three sixes in a ten-ball 23 - including two off new England call-up Tymal Mills - before becoming Shahzad's third victim in the final over as Gloucestershire set a testing target of 184 for 4.
Sussex made a positive start to the chase but lost opener Chris Nash for 13 when he top-edged an attempted sweep off Graeme van Buuren for 13.
The Sharks were 50 for 1 after the powerplay but suffered another blow when youngster Phil Salt was trapped lbw for 12 attempting to reverse-sweep Tom Smith.
Smith also pinned New Zealand international Ross Taylor in front for 16 which increased the responsibility on Wright's shoulders.
The Sussex skipper responded by bringing up his 50 from 38 balls and then launched Howell and Kieran Noema-Barnett for enormous sixes down the ground.
The game swung significantly back in Gloucestershire's favour, however, when Wright perished going for another maximum as he picked out the fielder on the midwicket boundary off Howell.
That left Sussex requiring 62 from the last five overs with two new men at the crease and it proved too tall a task despite Machan offering brief hope with three towering sixes.