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Gills suffered the agony of conceding a winning goal in the final seconds of second half stoppage time at Portsmouth.
Home defender Alessandro Zamperini stole in at the far post to head home and break all Gillingham hearts.
The visitors had deservedly taken a 34th minute lead through Iffy Onuora and were indebted to goalkeeper Vince Bartram for saving a 23rd minute penalty from Robert Prosinecki.
Pompey levelled in the 59th minute through Neil Barrett, before Zamperini snatched the winner.
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