Essex 304 for 7 (Westley 93, Zaidi 72*) beat Hampshire 279 (Vince 68, Bailey 63, Wagner 4-41) by 25 runs
Tom Westley's hard-hitting 93 off 98 balls helped set up Essex's 25-run victory in their first Royal London Cup match of the season.
Westley shared partnerships of 103 with Alastair Cook for the second wicket and 60 with Varun Chopra for the third as Essex threatened at one stage to run riot.
But they were pegged back mid-innings and were grateful to Ashar Zaidi's entertaining unbeaten 40-ball 72, which included four sixes, his highest List A score for Essex, for taking their score beyond 300.
Behind the run-rate throughout, Hampshire were always in the game while James Vince (68) and George Bailey (67) were at the wicket in a stand of 91 for the third wicket. Once they departed Hampshire fell further adrift and finished 26 runs short.
It hadn't started well for Essex, put in by Hampshire. Third ball, an inswinger from Reece Topley caught Nick Browne in no man's land and bowled him. It proved costly as both Cook and Westley went on the offensive. The former England captain drove Kyle Abbott for two fours and Westley pulled Topley disdainfully through midwicket.
Westley hit Topley out of the attack with three fours in four balls, the second of them through midwicket bringing up the 50 in the ninth over. Westley's own half-century came up off 45 balls with eight fours before a sweep off Mason Crane took the partnership to 100 in the 18th over.
But three runs later Cook departed when he moved down the pitch, while taking a step back to leg, and completely missing one from Liam Dawson.
Chopra reverse-swept and nurdled his way to 26 before he nibbled at one from Abbott and was caught by a tumbling Lewis McManus. Five balls later and Westley's bludgeoning innings was over, caught magnificently at midwicket by Bailey off Dawson.
Ravi Bopara struck a six off Dawson, the pick of Hampshire's attack, but was fifth out soon after, lbw to Crane for 10, before Ryan ten Doeschate was run out, scampering a quick single off and not beating Crane's throw.
Adam Wheater and Zaidi improvised in a partnership of 42 for the seventh wicket, Wheater's ramp shot off Gareth Berg earning a pat on the back from the bowler, and Zaidi going down on one knee to carve Crane over midwicket for six. But then Wheater played across one from Sean Ervine and lost his leg stump.
It was left to Zaidi to take Essex over the 300 mark with a spectacular exhibition of swashbuckling batting. He cleared the catering tent at midwicket off Ervine for a second six and reached a 30-ball half-century with an unorthodox third six over third man.
Hampshire's chase after 305 started just as Essex's had done. Michael Carberry got an inside edge to Neil Wagner's fifth ball and turned to see the off-bail on the ground, his second first-over dismissal in successive innings. Hampshire had only progressed to 36 in the eighth over when Tom Alsop lost his middle stump to one that swung in late from Matt Quinn.
Vince set about the recovery and hit both Quinn and Wagner off his back-foot for trademark boundaries square on the offside while Bailey opened up with straight sixes over the sightscreen off Simon Harmer and ten Doeschate.
Vince's fifty came up from 56 balls at the same time as the 50 partnership with Bailey. The stand was eventually broken when Vince gave a return catch to Bopara. Bailey took up the cudgels and duly reached his half-century from 47 balls.
Dawson gave support in a 55-run partnership before he was run out trying a single to Browne at wide mid-off. Next ball Wagner had Bailey caught behind and suddenly Hampshire had slipped from 182 for 3 to 182 for 5 with 17 overs left.
Hampshire needed 87 off 66 balls, 79 off 53 and 63 off 42, but Ervine struck Quinn over midwicket for a six that brought up the fifty stand with McManus. But Ervine, the non-striker, was caught of his ground shortly after by ten Doeschate to make it six down for 242.
The Essex captain then claimed Gareth Berg to a caught-and-bowled and McManus to a catch on the long-leg boundary. Wagner wrapped things up with two wickets in two balls, having Abbott caught at long leg and Crane bowled to finish with 4 for 41.