Shoaib Malik top scored with 50 for the Bears, but Worcestershire's prolific captain Daryl Mitchell made 62 not out at the top of the order as his side won by eight wickets, with more than five overs to spare.
The number eight smashed 33 from only 13 deliveries as the home side knocked off 154 with two balls remaining, with Mark Pettini (42) and skipper Ryan ten Doeschate (34) also chipping in with important runs.
Middlesex may have made more than their 153-5 had Neil Dexter not ran out partner Eoin Morgan when the England star was flying on 69 off 46 balls, with the rest of the Panthers struggling to get going.
It also went right down to the wire at The Ageas Bowl, where Hampshire made 180-6, with captain Jimmy Adams leading from the front with 69 not out, well supported by James Vince (39) and Glenn Maxwell (30).
Tom Smith smashed four boundaries in a quickfire 30 as he and Howell nearly took Gloucestershire over the line, but the visitors fell two runs short, with Will Smith (3-26) the pick of the Hampshire attack.
Andrew Flintoff did not feature for Lancashire Lightning, but the Red Rose still cruised to a 57-run win over Northants Steelbacks, with Jos Buttler hitting three sixes in a 26-ball knock of 58, as they posted 187-3.
Northants lost early wickets and never recovered as Junaid Khan starred with the ball, taking 3-16 as the visitors, who are letting their promising start to the campaign slip, fell to 134 all out at Old Trafford.
Sussex Sharks also got plenty enough batting first, with Luke Wright making 85 out of their 149-8 against Kent Spitfires, who were rolled for 114, with Steffan Piolet adding three wickets to his red inker.
Leicestershire Foxes (178-6) beat Durham Jets (177-7) by four wickets.
Worcestershire Rapids (134-2) beat Birmingham Bears (133-8) by eight wickets.
Nottinghamshire Outlaws (206-5) beat Derbyshire Falcons (179-7) by 27 runs.
Lancashire Lightning (187-3) beat Northants Steelbacks (134 a/o) by 53 runs.
Surrey (165-5) beat Glamorgan (148-8) by 17 runs.
Essex Eagles (157-8) beat Middlesex Panthers (153-5) by two wickets.
Hampshire (180-6) beat Gloucestershire (178-8) by two runs.
Sussex Sharks (149-8) beat Kent Spitfires (114 a/o) by 35 runs.