If they win their final two games - against Hampshire and Lancashire - they will finish top after yesterday's success enabled them to leapfrog over the Red Rose side.
Defending a total of 211 for 6, the Royals looked poised to win as they reduced Essex to 103 for 5 in the 21st over but the game went to the last ball.
Essex quickly lost their big guns, including Stuart Law who made 45 from 38 deliveries, but they were revived by Paul Grayson and Robert Rollins.
They put together a sixth-wicket stand of 87 before Grayson was dismissed by Richard Illingworth for 66 with 22 required from 22 deliveries.
It came down to nine wanted off the final over by Alamgir Sheriyar, and in it he got rid of Rollins for 51 and David Thompson to finish with 4 for 42 from five overs.
Gavin Haynes also took four wickets, including the valuable one of Law as he drove into the safe hands of Graeme Hick at short extra cover.
Tom Moody and Elliott Wilson launched the Worcestershire innings with an opening stand of 99 in 21 overs.
Moody was then stumped for 42 but Wilson went on to gather 60, containing seven boundaries, before he was caught on the deep midwicket boundary to provide the off-spinner Peter Such with one of his three wickets.
Yorkshire Phoenix moved out of the bottom three in the First Division and at the same time increased Leicestershire Foxes' relegation fears with a seven-wicket win with 12.2 overs to spare at Scarborough.
Vince Wells won the toss but saw his top batsmen fail as they were restricted to 139 for 9. Chris Silverwood continued his fine form with 3 for 16 in 9 overs and he was well supported by Ryan Sidebottom and Craig White.
Yorkshire were given an aggressive start by White, who hit 28 from 29 balls and put on 50 with Michael Vaughan (41) for the first wicket.
Richard Blakey fell for a single but by then Yorkshire were close to victory and they were hurried on by Anthony McGrath, who hit a six and three fours in an unbeaten 24 from 17 balls. He drove a Tim Mason no-ball for four and then lifted the free hit over long off for six.Reuse content