Obafemi Martins let rip a stinging shot from just past the halfway line within minutes of the kick-off to test James, who squinted and saved in the bright sunshine.
Fellow African Geremi then tested James shortly after, with a free-kick-come-cross from the right side of the area, as Newcastle took an early grip on the game.
The difficult light caused problems again for the cap-wearing James, who rushed out of his area only to completely miss an attempted clearance on the right wing with 14 minutes played.
Keegan was content with a point
Portsmouth then snapped into life when Papa Bouba Diop struck a poor shot wide from outside of the area and Steve Harper was forced to come running from his line to cut off the on-rushing Defoe soon after.
With both sides now settled, the midfields began to cancel each other out, with only half chances falling to Viduka and Nwankwo Kanu.
Viduka then forced a save from James when he volleyed in a ten-yard shot from a corner.
Kanu countered by driving a shot into the foot, then onto the arm, of Steven Taylor at the other end.
The second half continued in much the same vein when the competitive midfield battle temporarily sidelined Diop with a foot injury.
Redknapp heaped praise on David James
But with Diop back on the field Portsmouth broke when Defoe peeled away from his marker and collected a thirty-yard pass only to shoot wide from inside the area.
Joey Barton then played a slide-rule pass to release Martins in the Portsmouth area, who shot accurately from a narrow angle only for James to save well at the near post.
Johnson and Kanu then combined well 15 minutes after the restart, as the right-back broke in from the wing to complete a one-two before flashing his shot over the bar.
Johnson was involved again as Portsmouth broke from a Newcastle corner to release Defoe, who forced a strong-armed save from Harper.
Owen then had the chance of the game with 15 minutes remaining.
The diminutive striker shot from five yards after Portsmouth had failed to clear Newcastle's tenth corner of the game, only for James to superbly steer the ball over the bar as the ball bounced off his face.
Portsmouth had switched off and needed a good save from James minutes later to deny Geremi's bending 20-yard from giving the visitors the lead.
Both teams still pressed for a winner, though neither could muster another shot on goal.
• Portsmouth manager Harry Redknapp:
"If you said to me at the start of the week, win at Wembley, win at West Ham and take a point today, I would've been only too pleased.
"I just want to win the FA Cup - that's all that matters now to be perfectly truthful.
"If you said to me finish fifth or win the FA Cup, I want to win the Cup. I thought the pitch was difficult and wasn't conducive to great football."
• Newcastle manager Kevin Keegan:
"I think both Harry (Redknapp) and myself will look at it probably the same: could've won it, could've lost it.
"If we're honest, on the day a draw was right, but a 0-0 draw, I'm not sure.
"There were an awful lot of chances, but a combination of good goalkeeping and players being over-hasty, they were missed and it's a 0-0.
"I don't think I can come here and say we deserved to win but we certainly deserved at least a draw."
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