However, Spurs might have conceded the first goal had Paul Robinson not been able to scramble back to his line and tip over Spurs old boy Davis's sublime 25-yard chip.
That was a rare threat from the visitors, who set themselves up with a solid bank of five midfielders and seemed content to play for a draw.
Had striker Jermain Defoe been available - red tape following his deadline day move from Spurs to Pompey denied him - perhaps Pompey may have played with greater adventure.
But Pompey keeper David James would have been pleased by his side's defensive efforts.
The England keeper would also have been relieved that, early on, he managed to clear the ball to stop Keane stealing in after he had cheekily crept up from behind the goal-line.
After the break, the game remained open - and continued to be played out in alternate spells of sunshine and snow.
But if the weather was unpredictable, sadly the football was not as Pompey were able to read Spurs' attacking intentions and nullify them with relative ease.
It sparked a change from Spurs and, on 70 minutes, Bent and Jamie O'Hara replaced Dawson and a below-par Aaron Lennon.
But it was Portsmouth who almost made the breakthrough when Glen Johnson 's long pass released Kanu but the Nigerian headed weakly past Robinson, allowing Didier Zokora to clear. However, Bent then took the game by the scruff of the neck and settled matters in the space of two minutes.
First, Spurs' record signing nodded in from six yards after Berbatov's miss-hit shot bounced up invitingly.
And then two minutes later, Bent's trickery on the left flank gave him room to cut in and deliver a low cross which O'Hara slotted into an empty net.
Tottenham coach Gus Poyet: "Darren Bent opened Portsmouth up when he came on.
"He would like to be starting games and scoring goals but he made a big impact and that shows the importance of substitutes.
"It was a difficult game and we had to be patient, concentrate and know that sooner or later we would get our chance."
Portsmouth manager Harry Redknapp: "For 80 minutes we were right in there and I felt we'd taken the best that Tottenham could throw at us.
"I was thinking it was going to be a great point for us after making six enforced changes.
"Tottenham is not an easy place to go to after making changes like that, and I thought we were fantastic. The lads who came in did a good job and worked hard."
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