Villa were made to work hard for their victory and had to come from behind for the points after Michael Brown put Pompey ahead after 10 minutes with his first goal for the club.

John Carew pulled Villa level seven minutes later before he saw a penalty saved by David James later in the first half.

Villa dominated after the break and were finally rewarded when Delfouneso, an 80th minute substitute, swooped less than two minutes after his introduction to spare Carew's blushes and hand Villa all three crucial points.

The result saw Martin O'Neill's side leapfrog Liverpool into sixth place, six points behind fourth-placed Tottenham with four games to play. Pompey remain rock bottom with 15 points to their name.

In an open and entertaining first half, Pompey drew first blood after just nine minutes when Anthony Vanden Borre raced onto Kanu's through pass before beating Stephen Warnock and delivering a cross from the by-line. Kevin-Prince Boateng's delightful stepover allowed Brown to come onto the ball and fire past Brad Friedel in the Villa goal.

The visitors responded well to going behind so early and Carew missed a glaring opportunity to cancel out Brown's opener on the quarter-hour mark. The Norwegian hit Gabriel Agbonlahor's cross-shot straight at James, when putting it an inch either side of the keeper would surely have brought a leveller.

But Carew did not allow that miss affect his confidence and just a minute later he made amends with a tremendous finish after springing the offside trap to run onto Warnock's ball through. The striker cut inside the covering Marc Wilson before firing into the top corner, leaving James no chance.

Villa grew in stature as the first half wore on and they were only denied a second by the woodwork on 20 minutes, Wilson putting against his own upright from a dangerous Ashley Young cross towards the near post.

Profligacy was to return to Carew's game on 40 minutes, when referee Lee Probert pointed to the spot for Papa Bouba Diop's clumsy trip on the big man in the box - he struck the ball true enough, but it was too close to James, who was able to repel his effort from 12 yards.

Both sides had had earlier penalty shouts dismissed - Pompey after Richard Dunne's 33rd minute trip on Boateng and Villa when Vanden Borre appeared to pull down Agbonlahor four minutes later.

After the break, Pompey's energy levels clearly dropped and their performance suffered as a result.

Villa were allowed to dominate proceedings, yet despite the near constant succession of crosses into the Pompey danger zone, the visitors were frustrated in their efforts to find a winner.

Pompey seemed content to sit back and soak up the pressure while waiting to hit on the break. And Avram Grant's tactics nearly worked when Boateng fired on target on 68 minutes, only to see Friedel save, and then when substitute Tommy Smith headed over the bar from a corner on 77.

Still, Villa looked far more likely to trouble the scorekeepers again and they were unlucky not to be awarded a second spot kick a minute after Smith's miss when James appeared to bring down Stiliyan Petrov in the box.

But the visitors' pressure finally told when Delfouneso guided the ball over the line with eight minutes remaining following James Milner's cross which was flicked on by another substitute Emile Heskey.

Villa could have gone on and scored a third but Ashley Young's overhead kick went the wrong side of the post, while Pompey may have nicked a point at the death when Joel Ward's poke from close range was saved by Friedel.

Mike Hytner / Eurosport