Although the odds are still stacked against Shoreham avoiding relegation, manager George Parris says he cannot ask more from his side at present.
Parris said: "We were quietly confident going into this match. The confidence is growing and it shows in the way we are playing.
"We have got the habit of winning now and it is a nice habit to have."
Marshall gave Shoreham an early lead but Chichester levelled through Chris Male and then missed a penalty.
James Emmerson put Shoreham back in front, only for Tony Stevens to level again. But Marshall struck five minutes from time to secure all three points.
There was also late drama at Hassocks where the hosts scored four times in the final 13 minutes to beat Pagham 4-0.
Scott Langridge started the ball rolling, James Laing scored twice and Ashley Low got the other.
Leaders Langney Sports cruised in 4-0 against crisis club Wick, though the under-strength visitors never stopped battling.
Matt Allen's pace earned him two first-half goals and Daren Pearce fired in from the edge of the box.
Pearce completed the tally after the break from a penalty won by new signing Steve Sargent, who came off the bench.
Sports also gave debuts to Jon Monteath, from St Leonards, and Jason Reed, from Portfield.
Jonas Templeman returned from injury to score what proved the winner for Littlehampton as they beat Three Bridges 3-2.
Danny Cook put Bridges ahead, but goals from Carl Lloyd, Derek Chester and an 88th-minute strike from Templeman put Marigolds in command. Matt Beeston replied a minute later to set up a tense finale.
Ringmer were made to rue missed chances as they lost 4-0 at home to Portfield.
Manager Richard Soan said: "We had enough chances to lead 3-2 at half-time. Mark Harman could have scored a hat-trick, while Tony Ropke and Simon Penney should have scored. But in the second half, we were poor."
Goals from Danny Horrell, Ashley Edwards, after a powerful run, Kevin Brook with a long-range effort and Jamie Musslewhite gave Portfield victory.
Eastbourne Town lost 4-1 at Redhill despite taking a first-minute lead through Matt Jones. The home side hit back through Ian Clements, Paul Otway, Ben Jones and Dave Mizon.
Selsey are through to their second cup semi-final after beating Whitehawk 2-1 to reach the last four of the John O'Hara League Cup.
Ian Ford scored twice in the first half, the first coming from Darren Lowery's cross, with Hawks replying on the hour mark through Tom Graves.
Selsey boss Danny Hinshelwood, who has masterminded a remarkable turnaround after taking over, said: "It is going really well. The local boys have really pulled together and hopefully we can take it on from here."
East Preston manager/chairman Carl Stabler was delighted to round off a busy week with a 1-0 win Sidley.
Peter Brackley crossed for Robbie Pearce to hit the 26th-minute winner which takes EP into the semi finals.
Lee Gibbs later hit a post and Sidley had a goal disallowed for offside.
l Unijet County League division two round-up in tomorrow's Argus
Converted for the new archive on 30 June 2000. Some images and formatting may have been lost in the conversion.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article