Worcestershire appeared to be cruising towards victory when Hampshire, chasing 308, needed 48 runs to win with 21 balls remaining and one wicket in hand.
Some big hitting from Andrew Neal took Hampshire to the brink of an astonishing success but, requiring five more off the final three balls, he edged spinner Fateh Singh behind to fall for 48 off 22 balls.
The late drama at New Road was in sharp contrast to events earlier in the day at Radlett, where Middlesex made short work of Glamorgan’s batting line-up.
Naavya Sharma (4-29), Toby Roland-Jones (3-35) and Noah Cornwell (3-1) were the only three bowlers used as Glamorgan, who were 44-1, lost their final nine wickets for 22 runs.
Josh de Caires hit 10 fours in his 45 not out as the hosts completed victory within three hours of the match starting.
At Hove, an early rain shower meant a slightly reduced match of 48 overs per side.
Opener Will Luxton made 117 in Yorkshire’s 325-7 and Coad’s four wickets with the new ball left Sussex on 21-5 as they chased a revised target of 325.
Coad ended with 5-12 from seven overs as Sussex were bowled out for 140 to lose by 184 runs on the Duckworth-Lewis (DLS) method.
Essex beat Derbyshire by nine runs at Chelmsford in the other match in Group B, with both captains leading their sides’ respective batting causes.
Westley, making his 500th career appearance in all formats, scored 102 off 97 balls in the hosts’ 257-7.
Harry Came (97) shared an opening stand of 113 with Martin Andersson but the match looked in the balance when Derbyshire needed 100 more with five wickets in hand.
Charlie Bennett (3-32) broke a seventh-wicket partnership worth 45 between Ross Whiteley and Nick Potts, which proved crucial.