Durham 153 for 4 (Stoneman 40, Mustard 40) beat Northamptonshire 149 for 5 (Cobb 68, Duckett 48) by six wickets
The scrap for qualifying places in the NatWest T20 Blast North Group hotted up further as one-time leaders Northamptonshire lost by six wickets to Durham at Chester-le-Street.
By maintaining their unbeaten home record, Durham strengthened their hold on fourth place with two of their remaining three games also at home.
But they turned a stroll into a scramble as they replied to 149 for 5 with an opening stand of 77 inside ten overs, then slipped to 89 for 4 with Ben Stokes falling for one.
Both he and Mark Stoneman were lbw trying to sweep Sri Lankan leg-spinner Seekkuge Prasanna, who also had Phil Mustard caught off a towering straight drive to finish with three for 24.
Both teams were on 100 after 14 overs, but whereas Ben Duckett was unable to accelerate in his unbeaten 48 off 42 balls, Keaton Jennings continued his excellent season by seeing Durham home with nine balls to spare.
He cut Rory Kleinveldt for six in making 36 not out off 24 balls and shared an unbroken stand of 64 with Michael Richardson.
That over from Kleinveldt, the 16th, included two wides and cost 15, one fewer than the ninth, bowled by Steven Crook. Bowling round the wicket to the left-handers, he began with a wide and conceded four leg byes with another leg-side ball before Mustard hit him for four and six over mid-wicket.
It was also a poor night for the competition's leading dot ball bowler, Richard Gleeson, who finished the match with a no-ball followed by a wide which flew down the leg side to the boundary.
Stoneman beat his season's previous best T20 score of 25 by making 40, as did Mustard.
Despite Josh Cobb hitting 68 off 51 balls, Durham kept a tight rein on the visitors after putting them in. Going in at 14 for 2, Duckett shared a stand of 95 with Cobb. But he lacked the firepower to take his side to a winning total.
Chris Rushworth knocked out Richard Levi's off stump with the first ball of the match and in the fourth over Adam Rossington went down the track to Mark Wood, only to sky a comfortable catch for Mustard.
Wood, whose four overs cost only 19, almost had a second wicket when Cobb, on 16, narrowly cleared mid-off. Cobb lifted Scott Borthwick over long-on for six then a lofted straight drive off Jennings gave him his fifth four and took him to 50 off 40 balls before driving Ryan Pringle for a straight six.
Cobb departed in the 16th over when he tried to scythe Jennings through off side and played on, then Crook went down the pitch to a slower ball and was stumped.
Kleinveldt scored 23 of the 35 runs which came off the last four overs, including a huge six over the sightscreen off Jennings, before he was caught by Wood at long leg off the last ball.