Somerset 237 (Abell 106, Archer 5-42) beat Sussex 227 for 9 (Groenewald 3-30) by 10 runs
A century from 22-year-old Tom Abell against Sussex at Taunton, helped Somerset to secure home advantage in the quarter finals of the Royal London Cup.
The young batsman batted without equal to score 106 off 117 balls, as Somerset held off a late revival from the Sussex tailenders, to win by 10 runs.
Somerset, having chosen to bat first, might have felt this was not to be their day having slipped to 15 for 2 inside four overs. Mahela Jayawardene and Peter Trego were the men out as 21-year-old Jofra Archer put Sussex in a commanding early position.
Jim Allenby's quickfire 30 was the dominant feature in a 32-run stand with Abell, for the third wicket. However, when the captain departed, once again off the bowling of Archer, Somerset were back in trouble at 47 for 3.
Despite the mounting pressure, Abell batted with great maturity and with the help of one or two middle order partners, took Somerset to a score that was respectable, if not altogether satisfactory.
He added 70 for the fourth wicket with James Hildreth and 42 for the eighth with Craig Overton. Although Lewis Gregory and Ryan Davies chipped in with useful runs, it was Abell who led the way. He posted his second List A fifty without too many alarms and finally passed three figures for the first time in one-day cricket, off 107 balls with nine fours and a six.
Ten balls later he was run out for a fine 106 as Somerset crept towards the 250 mark.
In the end, they fell 13 runs short of that milestone when Tim Groenewald became Archer's fifth wicket at 237. Archer finished with the impressive figures of 5 for 42 off 9.1 overs.
Although the 50-over season has been something of a damp squib for Sussex, to date, they would certainly have fancied their chances of posting a second win of the campaign, in this their penultimate game in the Royal London Cup.
Somerset, however, had different ideas and with Groenewald and 25-year-old Josh Davey leading from the front, with the ball, the visitors found themselves well and truly behind the black ball.
Opening batsman Philip Salt departed in the second over, without scoring, lbw to Davey, before Harry Finch was run out by the man of the moment Abell at 25 for 2.
It got worse. Captain Luke Wright became Groenewald's first victim at 59 for 3, and after Chris Nash had been trapped lbw, first ball, by Gregory, seven runs later, Groenewald returned to pick up the important wickets of Ed Joyce and wicket keeper Ben Brown.
When Chris Jordan became Trego's first victim at 95 for 7, Sussex were heading for a landslide defeat. However, Archer and Ajmal Shahzad added 61 for the eighth wicket to leave Somerset wondering whether 237 would be enough.
Archer, having struck two fours and as many sixes in his 35, was eventually bowled by Max Waller, who also took the wicket of Shahzad.
Will Beer and Danny Briggs did their bit to keep Sussex in with a chance of victory, adding an unbeaten 52 for the last wicket. However, it was not to be and in the end, Somerset kept their cool to not only make sure of victory, but to secure a home tie in the last eight.