Dan Lawrence, Mohammad Amir star as Essex beat South Group leaders

Sussex supporters packed into the tight confines of Hove on another sell-out T20 night had relished news of the Ashes exploits of Jofra Archer, but for once they had to make do with vicarious pleasures as they watched their side's hold at the top of South Group weakened by a nine-run defeat against Essex.

The South Group is now as congested as, well, most of the south, with Essex, who began the night in eighth place, still retaining hopes of a late rush into the top four. Only Glamorgan and Surrey can be discounted.

Essex's 168 for 5 represented a challenging target for a side that bases its success around a powerful bowling attack, but David Wiese's 66 from 36 balls - with Laurie Evans his most productive sidekick - took them within 39 with 28 balls remaining when he was sixth out, sweeping at Simon Harmer.

Wiese, one of T20s most experienced campaigners, has entered his Tarantino villain phase with vigorous beard, long hair and determined chew. His free-flowing straight six off Aaron Beard, backed up by two boundaries from misfields, had just taken 17 off Beard's last over, but he was unable to rescue the game.

Essex have the worst T20 record in the country in recent seasons (Sussex have the best), but they dug in well here, despite some shoddy fielding. All their bowlers played a part from Cameron Delport, who had bowled only three overs of medium-paced mix-ups all season but who slipped in two overs without much damage, and the diminutive Australian leggie Adam Zampa, complete with perfectly matching yellow headband, who had Will Beer caught at extra cover at the start of his last over with 23 needed off 18.

But it was Mohammad Amir, whose return of 4 for 29 stood out for Essex: another fine over, the 19th, included the dismissal of Chris Jordan, a flat-bat to Ravi Bopara at deep midwicket when the game was still there for the winning.

Sussex's openers, Phil Salt and Luke Wright, were also picked off during Amir's first two overs. Salt is a batting roulette wheel, capable of extravagant success and failure, and he toe-ended to mid-on. Wright could not control a pull at a ball he might have cut and spliced to mid-off.

Alex Carey has claims to be Australia's best batsman-keeper, but can't get in the side even though they are picking two of them: he fell to Beard as Bopara fell backwards at cover to take a catch that he claimed more confidently than he caught.

Poor old Harry Finch is having a season to forget. He has made a pair in his last two Championship matches, divided by a prolonged spell in the 2nd XI. His first T20 outing of the summer with Delray Rawlins absent with Bermuda brought another duck, first ball, as he was lbw trying to reverse-sweep Harmer.

Essex's general lack of success is hard to understand, especially now that Delport adds a rough-hewn power to the top of their order. They were looking sacrificial at 84 for 4 in the 12th over, but a stand of 82 in eight overs between Dan Lawrence and Bopara ensured a score to be reckoned with.

Sussex are not just managing without Archer. Tymal Mills is expected to miss the rest of the season with a stress fracture and legspinner Rashid Khan has moved on, but their ambition has been seen in the short-term acquisition of the Australian Jason Behrendorff, who took five wickets against England in a World Cup group game in June, for their last four group matches.

Behrendorff did not take a wicket but made his mark instead with the run out of Adam Wheater and a straightforward catch at long-off when Tom Westley, after making 34 from 25 balls, tried to get after the legspin of Beer. Beer is not quite the regular he was but his record in 107 T20s is a strong one and he followed up an impressive return of 3 for 22 against Surrey with 2 for 19.

Lawrence and Bopara broke Sussex's grip, however, with a stand of 82 in eight overs. Lawrence does not possess prodigious strength and his attempts at innovation did not always come off - especially against the wiles of Reece Topley - but his unbeaten 59 from 43 dominated Essex's innings, helped for four sixes, more or less straight, against Wiese and Danny Briggs.

Even more energising was Bopara's 45 from 24 balls. One six over the off side against Topley had him grinning with the umpire Alex Wharf about the audacity of a shot that he would have found wondrous enough at his peak. It took a magnificent tumbling catch at long-off by Jordan to silence him with two balls remaining.