AS the seagulls of summer circled above Hove, their shrill cries piercing the humid air, so Sussex swooped to snaffle the points.
Victory by four wickets was their third in successive CB40 games and cemented their place at the top of Group C.
Yorkshire, who fielded a near full-strength side on the sunny south coast, have now lost two of their opening three games.
With only one side progressing from each of the three seven-team groups, along with the best second-placed outfit, it already means there is little margin for error.
After winning the toss, Yorkshire scored 238-9 – a total that looked a good 30 runs short.
The top-six batsmen all made between 26 and 46, with no one making a sizeable score.
In contrast, Luke Wright (103) made a significant contribution as Sussex eased home with 37 balls to spare.
It was a chastening night for the Yorkshire bowlers – in particular new overseas signing Mitchell Starc, who conceded 0-71 from eight overs, including 21 from his opening over, the first of the reply.
In front of 4,000 spectators, Yorkshire showed one change to the side that beat Derbyshire on Sunday by seven wickets.
Ryan Sidebottom replaced Iain Wardlaw, who did not travel due to stiffness in his back.
Yorkshire captain Andrew Gale, who had not been expected to play due to a shoulder problem, recovered to take his place in the starting XI but was soon in the wars again after opening the batting.
Gale was struck on the helmet by a short delivery from Amjad Khan and although he duly recovered to complete his innings, he played no part thereafter due to the effects of mild concussion, with Australian Phil Jaques assuming captaincy duties.
After taking 16 deliveries to get off the mark, an unusual statistic for such a quick scorer, Gale found his feet when he savagely cut Chris Liddle for four and then uppercut Khan for six over backward-point.
With Adam Lyth blazing away at the other end, Yorkshire scored 43 runs in the opening eight overs of power play, but with a promising platform firmly established, Lyth continued his trend of getting out when well-set when he fell for 27 with the total on 49 in the ninth over.
The left-hander spooned off-spinner Chris Nash to mid-off, where Ed Joyce – deputising as captain for Michael Yardy, who injured a finger in practice the day before the game – claimed a simple catch.
Maddeningly for Yorkshire, Lyth had been dropped in the same position by Joyce earlier in the over when the former England man threw up a perfunctory right hand.
Jaques injected impetus, crashing consecutive boundaries off Nash – one insouciantly through mid-wicket, the other imperiously through cover.
But he and Gale made presents of their wickets: Gale bowled swinging across the line by Nash for 42 and Jaques dismissed for 37 when he chipped Monty Panesar languidly to mid-wicket.
Yorkshire slipped to 161-4 in the 29th over when Gary Ballance also failed to build on a promising start, caught by Joyce at mid-wicket off leg-spinner Will Beer.
Ballance had earlier played one of the shots of the match when he swung Beer out of the ground over the short leg-side boundary to the old press box side.
Joe Root and Anthony McGrath kept the scoreboard moving with a fifth-wicket stand of 65 in 49 balls, characterised by some delightful reverse-sweeps and paddles from Root.
McGrath perished three overs out when he launched Liddle high in the air and was caught by the wicketkeeper, Root following in the next over when he paddled Khan once too often and was caught by Panesar at long-leg, having made 46 from 36 balls with five fours.
The innings continued to subside when Azeem Rafiq edged his first ball from Khan to the wicketkeeper, Gerard Brophy was bowled round his legs by Liddle and Sidebottom caught and bowled by Khan, Yorkshire losing 5-11 in 17 balls.
There were no such wobbles from Sussex.
Starc’s first over was one to forget – Nash helping himself to four fours – and his second and third were not much better as his opening spell read: 3-0-34-0.
But when Starc returned at the Sea End, his first ball led to the fortuitous run-out of Nash, who was stranded at the non-striker’s end when Starc diverted Wright’s firm straight-drive on to the stumps with his boot.
Sussex slipped to 87-3 when Moin Ashraf had Murray Goodwin well caught at slip by Ballance, but Wright and Gatting thwarted the visitors, adding 90 in 15 overs before Gatting skied Root to deep mid-wicket.
After Root had Matt Machan caught at mid-wicket, Wright completed his second domestic one-day century before being run-out with four runs needed by a smart piece of fielding from Lyth at mid-wicket.