Albion were held to only their second Withdean draw of the season against relegation-threatened York.
Gary Hart gave the Seagulls the lead with his seventh goal of the season on 55 minutes.
Micky Adams' men looked on course for three more valuable promotion points at that stage, but they were ahead for only 13 minutes.
Skipper Steve Agnew levelled in cool fashion for the visitors to leave another near-capacity crowd disappointed.
Albion laboured in the first half until Adams made a substitution.
Paul Brooker was brought on after 36 minutes in place of Kerry Mayo, who is banned for next Saturday's visit to Leyton Orient.
Brooker had an immediate impact, forcing Alan Fettis into a couple of smart saves.
Albion looked like chiselling out their ninth win out of ten at Withdean when Hart put them in front with his first goal since Boxing Day.
His initial effort from Andy Crosby's low cross was blocked, but he scored with a left foot shot on the turn.
The threat from York appeared to have evaporated following Brooker's arrival, but the balding Agnew grabbed an equaliser out of the blue.
The former Sunderland and Leicester midfielder ghosted through a static defence from Wayne Hall's cross before side-footing past Michel Kuipers from point-blank range.
Bobby Zamora had a game to forget on an afternoon when several Albion players were below-par.
The 20-goal hotshot headed wastefully over from a Paul Watson corner and then miskicked late on when well placed.
The final whistle was greeted with mild booing as the Seagulls reflected on two points dropped.
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