Second half goals from Jasper Pattenden and Callum Kealy secured the win for the hosts, who never looked in danger of losing.
Both sides progressed to this stage courtesy of 3-2 victories back in December: the Mackerel Men overcame Cray Wanderers at Woodside Road, and the Tanners won away at Ramsgate.
The tie began with a quiet opening quarter, with both sides testing the waters as they settled into their rythms.
Leatherhead keeper Zaki Oualah was forced into action for the first time in the 20th minute, through a rasping Jasper Pattenden effort. Pattenden carved out a yard of space 20 yards from goal and fired his shot towards the bottom right corner, but Oualah was equal to it.
This proved to be the only chance of real note in the first half. It was a frustrating 45 minutes for both teams. A real war of attrition was taking place in the middle of the pitch, with territory being gained inch by gruelling inch, and plenty of free kicks being conceded.
The visitors had a good chance to break the deadlock early on in the second period, as a 2-on-1 breakaway chance presented itself after a Worthing corner, but Cam Tutt put in a brave last-man challenge to put a stop to the attack.
The game finally sprung into life after 65 minutes, as Worthing started to mount some pressure on the Leatherhead goal. Substitute Tom Chalaye had a couple of good sights of goal: he almost latched onto a loose ball 6 yards from goal but the Leatherhead defence cleared it, and Chalaye’s flick from the resulting corner forced a great reaction stop from Oualah.
The deadlock was finally broken just moments later. Kealy ran to the byline and fired in a low cross, and Pattenden made no mistake from 6 yards to put the Mackerel Men ahead.
After so long without any chances, two came within two minutes. Joe Clarke drove towards goal, beating two men and finally being chopped down by a third, and the referee did not hesitate to point towards the spot. Kealy stepped up to take it, and slotted home off the base of the left hand post to double the host’s lead.
The visitors went close through Travis Gregory late on in the half, as the Leatherhead forward had a dig from 25 yards and his curling effort went narrowly past the upright.
Left back Lema forced Carl Rushworth into his first save on the 90th minute, with the defender curling a strike towards the far post and drawing Rushworth into a fine save.
That proved to be the final chance of the game, and Worthing ended up comfortable 2-0 winners after a much improved second half display.