Mohammed Salisu saw his marching orders for a second yellow card 15 minutes after James Ward-Prowse had given Southampton a deserved 1-0 lead.
The clumsy foul, which had left Son Heung-Ming on the floor, gifted Spurs a way back into the match as Harry Kane calmly converted from the spot in the 41st minute.
Up to that point, Southampton boss Ralph Hasenhuttl’s tactic to switch to a back three formation had stumped Spurs.
Son and Kane each had half chances from distance after falling behind, but collectively they were unable to crack the Saints defence from open play.
Southampton was again without Jack Stephens and Lyanco — both out due to COVID-19 health and safety protocols — with Yan Valery and Salisu slotted either side of Jan Bednarek.
Huge shift, @yan_valery— Southampton FC (@SouthamptonFC) December 28, 2021
His thoughts on a well-earned point:
Kane thought he had doubled his tally eights minutes after the restart, but had his goal ruled out for offside in the slightest of margins.
Spurs were again thwarted by the whistle after Matt Doherty hit the back of the net in bizarre fashion with the ball squirting between he and goalkeeper Fraser Forster, only for Anthony Taylor to blow for a foul.
Doherty was then denied one-on-one with Forster after his overlapping run freed him down the right before Forster made a save with his right leg to prevent the breakthrough.
Second-half substitute Armando Broja had a chance to steal all three points for Saints in added time, but had his shot blocked over the bar.
With four points from their last two games, Saints climbed into 13th in the table and 10 points above 18th place Burnley who have four games in hand due to postponements.
Saints will be without defenders Salisu and Kyle Walker Peters (accumulation) for their January 2 tilt with Newcastle.
Southampton (5-3-2): Forster; Perraud, Salisu, Bednarek, Valery, Walker-Peters; Ward-Prowse, Diallo, S. Armstrong, A. Armstrong (Redmond 83), Long (Broja 71)
Unused subs: Caballero (GK), Walcott, Small, Simeu, Elyounoussi, Romeu
Goals: Ward-Prowse (25)
Bookings; Walker-Peters (13), Salisu (27, 30), A. Armstrong (51)
Tottenham (3-4-2-1): Lloris; Davies, Dier, Sanchez; Reguilon (Doherty 46), Hojbjerg, Winks, Emerson (Gil 77); Son, Alli (Moura 62); Kane
Unused subs: Gollini (GK), Tanganga, White, Rodon, Ndombele, Skipp
Goals: Kane (41 PEN)
Bookings: Reguilon (45+1), Winks (69)