Northamptonshire 180 for 4 (Zaib 70*) beat Worcestershire 178 for 6 (Cox 46*, Heldreich 3-28) by six wickets
Worcestershire Rapids missed out on the chance to make history as their unbeaten start to the Vitality Blast was brought to an end by Northamptonshire Steelbacks who triumphed by six wickets at New Road.
The Rapids had been bidding to win the opening five games in the T20 tournament for the first time. But Steelbacks spinner Freddie Heldreich bowled an inspired spell which brought him the wickets of Adam Hose, Brett D'Oliveira and Kashif Ali in the space of three overs.
Then Saif Zaib produced the fireworks with the bat for the visitors, smashing successive sixes in the final over from Pat Brown to see his side home with two balls to spare. He ended unbeaten on 70 from 35 balls with nine fours and two sixes to seal a third win in the last four games for the Steelbacks.
D'Oliveira, Jack Haynes and Mitchell Santner all made useful contributions with the bat for the Rapids but it was keeper Ben Cox who provided late momentum.
Fit again opener Ricardo Vasconcelos provided the Steelbacks with early aggression and then Saif kept his nerve to see his side over the finishing line.
Ben Sanderson broke through for the Steelbacks in the opening over as Michael Bracewell sliced a drive to short third man.
D'Oliveira got into his stride with successive boundaries off his Steelbacks counterpart David Willey. But he came close on 12 to being run out after playing Sanderson to midwicket and replays indicated he was short of his ground to Willey's direct hit.
Haynes survived two chances in an over from Tom Taylor, a low caught and bowled and then at short third man. He started to profit from these escapes in smashing a Sanderson full toss over the long on boundary and collecting two fours in two balls at Willey's expense.
Andrew Tye's introduction into the attack led to the downfall of Haynes who sliced a skier into third man's hands.
Hose, in prime form in recent games, tried to hit left-arm wristspinner Heldreich over the top and was taken at long-off. There was more joy for Heldreich when D'Oliveira made room to cut and only picked out backward point and it became three wickets in three overs as Kashif Ali departed in exactly the same manner.
Santner struck the ball sweetly in making 33 from 21 balls but then holed out to long-on after Taylor's return to the attack. Cox, with an unbeaten 46 from 29 deliveries, and Ed Pollock ensured a competitive total.
The Steelbacks were restricted to 14 runs from their opening three overs before Chris Lynn, a century-maker against Leicestershire on Friday evening, launched Brown over the long-on boundary. But Adam Finch brought his downfall when he could only find mid-on.
Vasconcelos seized on the introduction of spin for the final over the powerplay by striking Bracewell for three fours and a six.
Willey looked in good touch but again failed to capitalise on a decent start and sliced Santner to backward point. Bracewell came in for some heavy punishment but picked up an important scalp when Vasconcelos sliced the ball down deep cover's throat.
The Steelbacks looked in control while Zaib and Josh Cobb were together during a stand of 70 in eight overs.
Cobb eventually perished to Brown but Saif was up to the task of scoring 15 from the final over, despatching balls two and three over the ropes before crashing the next for the winning boundary.