Lancashire maintained the pressure on Group B leaders Hampshire by beating them in a Yorkshire Bank 40 thriller at Old Trafford.
The Lightning gained revenge for a Twenty20 quarter-final defeat by the Royals earlier this month with a five-run win which takes them within a point of the group pace-setters ahead of Monday's final round of fixtures.
A win for Hampshire away at Derbyshire would guarantee the defending champions a last-four place, but Lancashire stand to benefit from any slip-up if they beat Essex at Old Trafford.
Lancashire, who won the toss, put early pressure on under-strength Hampshire with a total of 261-9, built around half-centuries for Karl Brown, Steven Croft and opener Stephen Moore, who made scores of 66, 65 and 51 respectively.
Off-spinner Arron Lilley and Kabir Ali both took three wickets in the defence, including Ali defending 12 off the last over and seven off the last ball.
It was a spirited performance from Hampshire, who were without four key players to international commitments. Michael Carberry, James Vince and Danny Briggs are all with the England Lions and Sohail Tanvir with Pakistan in Zimbabwe.
Dimitri Mascarenhas took his best List A figures in more than 11 years - 5-42 - and 16-year-old off-spinner Brad Taylor returned 2-50. Taylor even struck with his third ball on his 40-over debut when he had Moore caught behind.
Brown and Croft shared a crucial 95-run stand for the fifth wicket to improve Lancashire's score from 127-4 in the 20th over.
Hampshire were behind the rate for the majority of their innings on a slow pitch even though they managed to keep wickets in hand. They needed 100 with 10 overs left and key men Neil McKenzie and Sean Ervine at the crease. They had shared 72 inside 10 overs for the fourth wicket, with McKenzie hitting 65 off 54 balls and Ervine 43 off 36.
But when McKenzie fell stumped to Lilley as the first of two wickets in two balls in the 35th over, Hampshire looked done. Liam Dawson followed to leave the score at 200-5.
But Ervine kept them in touch before falling caught off an Ali full toss with the first ball of the 38th as the scored slipped to 228-6.
Some impressive hitting from Adam Wheater and Mascarenhas took the equation down to 22 off the last two overs and 12 off the last before they also fell caught off Ali full tosses as Lancashire won for the sixth game in a row.