The Saints defender headed into an unguarded net in the last minute of injury time when of all people Antti Niemi had stolen upfield to hammer a rising shot against the bar which fell invitingly for Svensson to nod home.
A minute before that Jo Tessem had brought a fingertip save from Martin Herrera as Southampton suddenly realised they were in with a chance.
James Beattie rose at the back post to grab a Saints lifeline, but up until then Fulham had ruled the day.
Early Saints pressure came to nothing and it was Fulham who brought the best out of Niemi with two fine stops from Steve Marlet.
First the French forward had sent a glancing header towards the corner of the net on 21 minutes, but the keeper flung himself to his right to tip the chance away.
Then ten minutes later he was again on target when he latched on to a Steed Malbranque through ball, but once again Niemi was equal to the effort and diverted the ball around the post.
Southampton's best chance up until then came when Herrera, making his full debut, came charging out of his goal on 38 minutes to attempt a clearing header only to leave Matt Oakley with a difficult half volley from 25 yards which drifted over the bar of the unguarded goal.
Just after half time Jason Dodd nearly became a scorer, against his own team.
The captain's pass back bounced awkwardly and only Niemi's presence of mind allowed him to head the ball against his own bar and them calmly bring it under control.
There was nothing tranquil about the Saints defence for Fulham's second. Saha drilled the ball low into the box only for Svensson to collide with the cross and divert it into his own net.
However he had Niemi to thank for sparing his blushes.