Nigel Quashie's first goal for Southampton earned a precious win in their survival bid and avenged their earlier 5-1 defeat at Tottenham.
Quashie thumped in a close-range header from Mikael Nilsson's cross and Saints then defended doggedly and at times desperately to preserve their lead.
Goalkeeper Paul Smith was again in top form, denying Spurs with a string of superb saves.
He saved his best for last, spreading himself to deny Frederic Kanoute.
Within a minute, Spurs almost broke their unenviable record of never having scored in four league and cup visits to St Mary's.
But Smith, who preserved a precious point for his side against Arsenal, kept Saints alive with a save from Mido.
Not surprisingly the Egyptian striker and Andy Reid were both booed by Southampton supporters after opting to join Spurs in the transfer window instead of Saints.
That set the pattern for a lively first half where an array of striking talent failed to take advantage of defending from both sides that was less than convincing.
Defoe (right) gave Danny Higginbotham plenty to think about
Smith again proved on top of his game and kept Southampton in touch with a fine save from Jermain Defoe who cashed in on Danny Higginbotham's error to break clear.
Mido blasted the ball across goal when a subtle touch to Reid was required but Spurs' defence was twice caught out by long balls from Olivier Bernard using Henri Camara's pace.
England keeper Paul Robinson arched up to block the Senegal striker's attempted lob, but was then relieved as Camara again escaped and crossed to the near post where Peter Crouch toe-poked the ball inches wide.
Southampton appeared to have suffered a blow when Rory Delap limped off but it proved a godsend.
Substitute Nilsson's first contribution was to whip in a pinpoint cross for Quashie to score his first goal for Saints with a thumping header.
The keepers continued to star, with Smith denying Defoe within a minute of Saints taking the lead, and Robinson saving point-blank from Crouch's header.
Defoe was mounting a personal crusade to pull Spurs level with his pace, but there was always a Saints defender willing to throw himself in the way to block.
Southampton defended ever deeper in their desperation to preserve their lead, and it was a dangerous game to play as Spurs dominated, and slung on Kanoute and Robbie Keane to give them a three-pronged strike-force.
Saints boss Harry Redknapp:
"It's going to be tight but the gap is starting to close and it wouldn't be the first time that somebody has been sucked in.
"For the first time, one or two teams will be starting to look nervously over their shoulders.
"This was a fantastic result for us, it was all hands to the pump at times."
Spurs head coach Martin Jol:
"We had four one-on-ones with the keeper and we should have got at least a draw.
"Their keeper was an amazing shot stopper but we should have put at least one into the net.
"We always create chances because we have good strikers, but they didn't score today and they know that."
Southampton: Smith, Delap (Nilsson 50), Lundekvam, Higginbotham, Bernard, Telfer, Redknapp, Quashie, Le Saux (Anders Svensson 88), Camara, Crouch.
Subs Not Used: Phillips, Cranie, Blayney.
Goals: Quashie 51.
Tottenham: Robinson, Kelly (Ziegler 68), Gardner, King, Edman, Davies, Brown, Carrick, Reid (Keane 75), Defoe, Mido (Kanoute 57).
Subs Not Used: Cerny, Pamarot.
Booked: Edman, Brown.
Referee: P Walton (Northamptonshire).