Yorkshire 156 for 6 (Williamson 48, Ballance 33) beat Warwickshire 154 (Porterfield 48, Evans 37) by two runs
Yorkshire Vikings recorded a remarkable victory over Birmingham Bears to keep their T20 Blast hopes alive after the visitors collapsed dramatically in the final overs.
Having been set 157 to win by at Headingley, Birmingham looked set to move to within a point of North Group leaders Northamptonshire with victory when they required 16 to win from 13 balls with six wickets in hand.
But David Willey and Tim Bresnan bowled superbly at the death before Adam Lyth's acrobatic fielding on the boundary denied Ateeq Javid the boundary needed off the final ball to tie a topsy-turvy encounter.
Despite a huge six from Lyth in Rikki Clarke's opening over, Yorkshire struggled to find the boundary in their six-over powerplay after winning the toss as the Birmingham seamers restricted them to just five boundaries.
The frustration got the better of both Lyth and Willey, with the pair both being caught in the ring off the bowling of former Yorkshire paceman Oliver Hannon-Dalby as the hosts fell to 34 for 2 early on.
Captain Alex Lees offered some resistance with 23 before being bowled by leg-spinner Josh Poysden, leaving senior duo Kane Williamson and Gary Ballance to rebuild through the middle overs.
The pair added 78 for the fourth wicket from just 59 balls before Ballance - who was celebrating his recall to the England Test squad to face Pakistan next week - was bowled for 33 by Clarke in the 18th over.
Williamson followed him back to the dug-out after running himself out for 48 in the final over, but some lusty blows from Bresnan and Jack Leaning lifted the Vikings to a total of 156 for six. Hannon-Dalby proved to be the pick of the bowlers, taking two for 33 from his four overs.
Birmingham's reply got off to the worst possible start as Sam Hain was adjudged LBW after attempting to shoulder arms to Willey's first legal delivery, but the Bears recovered thanks to a 50-partnership between Ian Bell and William Porterfield.
The former hit four fours on his way to 30 from 26 deliveries, but he fell victim to Adil Rashid in the leg-spinners first over as he advanced down the wicket and was stumped by Andrew Hodd.
And the England limited overs star was not finished there as he removed Australia wicketkeeper Matthew Wade for just six on his Blast debut with Lees taking a simple catch at backward point.
A stand of 60 between Laurie Evans (37) and Porterfield (48) looked to have swung the game back in Birmingham's favour, but their departures sparked an almighty collapse that left Javid needing to hit a four from Bresnan's final ball to force a tie.
His aerial drive over mid-on looked to have done the trick, only for Lyth to stretch his body over the boundary to drag the ball back inside the rope and force a run out as Birmingham lost their final six wickets for 13 runs in 13 balls.