Gus Poyet claimed a late dramatic winner for Spurs as they came out on the right side of a seven-goal thriller.
Spurs had taken the lead three times through Jermain Defoe on his debut and Robbie Keane (2).
But each time Pompey came back with Eyal Berkovic, Lomana LuaLua and Ivica Mornar on target.
But Poyet's shot from Dean Richards' header gave Spurs victory and eased the pressure on manager David Pleat.
Spurs, and new signing Defoe in particular, had the perfect start with the opener after 13 minutes.
Ledley King made the break and set up Robbie Keane who found Defoe, his shot creeping through Shaka Hislop's legs into the bottom left-hand corner of the net.
Spurs should have added to their tally on 24 minutes with Simon Davies finding himself through, but Hislop came out to smother Davies' less-than convincing shot.
13 mins: Jermain Defoe claims a debut goal for Spurs
39 mins: Eyal Berkovic levels it up
41 mins: Robbie Keane restores the lead for Spurs
73 mins: A debut goal for Portsmouth's Lomana LuaLua levels it again
78 mins: A spectacular solo goal by Robbie Keane gives Spurs hope again
84 mins Substitute Ivica Mornar gets another equaliser
89 mins Gus Poyet claims a dramatic winner.
Stephane Dalmat began to impose himself and did well set to set up Keane but the Republic of Ireland international could not make anything from his shot.
Spurs paid the price five minutes before the break when Berkovic fed Aiyegbeni Yakubu and raced into the six-yard box for the return.
Yakubu crossed deep and low and Steven Carr's attempted clearance hit Berkovic on the head and went over the line for his first Premiership goal since November 2002.
But Portsmouth's joy was short-lived as Keane showed his class yet again with a stunning goal after 41 minutes, his sixth goal in five games and 12th of the season.
He had his back to goal on the edgeof the box when he turned and rifled home a left-foot volley.
But the old Spurs frailities that in midweek saw them throw away a three-goal lead to Manchester City before losing to a last-minute strike, returned early in the second half.
First Berkovic saw his free-kick go just past the post and then Nigel Quashie was narrowly off-target with a good effort.
LuaLua, a second-half substitute for Amdy Faye went close for Portsmouth on 66 minutes after a neat passage of play with Yakubu and Berkovic but Keller did well to save.
But the substitute finally got his reward on 73 minutes when he turned on the edge of the box and sent a right-footed shot goalwards to make it 2-2.
With the home fans booing defender Dean Richards, it looked like Spurs would crumble,
However Robbie Keane ensured that the home side were not finished, waltzing through the Portsmouth defence to put Spurs back into the lead just five minutes later.
Another Portsmouth substitute Ivica Mornar had what looked to be the final say with six minutes to go when he bundled home LuaLua's cross from the left.
But after losing their seven-goal Cup thriller to City, Spurs were determined not to make the same mistake twice.
A corner from the left by Davies was headed back across goal by Richards and the ball went in off Poyet's knee for the points.
Tottenham: Keller, Carr, Gardner, Richards, King,
Dalmat (Ricketts 73), Davies, Brown, Jackson, Keane,
Defoe (Poyet 82).
Subs Not Used: Burch, Doherty, Yeates.
Portsmouth: Hislop, Curtis, Primus, Taylor, De Zeeuw, Faye (LuaLua 64), Quashie, Berkovic (Stone 85), Smertin, Sheringham (Mornar 45), Yakubu.
Subs Not Used: Wapenaar, Berger.
Referee: P Walton (Northamptonshire).