Chichester City had a bad week after a surprising last-minute league defeat to Sidley United and a Sussex Senior Cup second-round exit at East Grinstead Town.
After starting 2011 with a derby win at Selsey, City were disappointed on their return to Oaklands Way.
Michael Turvey was allowed space in the Sidley box to poke home the opener early on, but Daniel Spice rose highest to head in the equaliser for the visitors on 45 minutes.
That gave Sidley the momentum to push on in the second half, Chichester keeper Matt Short being called upon to make several saves before Jason Taylor rounded him but failed to find a finish.
Liam Miles popped up in the 90th minute to volley in the winner via the crossbar to condemn City to their first defeat in six games.
Chichester are still fourth in the table.
On Tuesday there was no respite for the Oaklands Way outfit as they were comprehensively outplayed by East Grinstead, who ran out comfortable 3-0 winners over ten-men Chichester in the county cup.
EG hit second-half goals through Rikki Cable, Liam Baitup and Danny Beszant as well as striking the woodwork twice in the game. And when Lloyd Anthony broke clear of the Chichester defensive line, Rowan Wallis brought him down and the youngster was shown his first red card of the season.
Chichester go to Lingfield on Saturday.
CHESTER BROWTON & MARK ALLAWAY