After six successive away defeats, keeping their first clean sheet in 14 games was another vast improvement for new Pompey boss Alain Perrin, who was delighted by his side's battling display.
"We came here to get a point but after 50 minutes we were looking for more points," said the Frenchman.
"Birmingham were more aggressive but we more than deserved our point. I am now looking for another five points from our remaining games, but we face a difficult week with two games against Liverpool and Southampton.
"But having to play Birmingham without several key players I am pleased with our performance."
This view was shared by full-back Andy Griffin, who gave a stalwart display for Pompey. He said: "We battled hard and overall we deserved a point off a Birmingham side who are always difficult to beat."
Following their third goalless draw of the season Birmingham boss Steve Bruce honestly admitted: "It was agony, absolute agony. And painful to watch.
"What was disappointing for me was the fact that we again struggled to take points off a team below us in the Premiership.
"It wasn't a case of a lack of motivation. The game cried out for someone to put their foot on the ball and take control. I cannot say it was a game we should have won because Portsmouth scrapped and deserved their point."
Loan star Jermaine Pennant, who is expected to agree terms this week for a close season move from Arsenal, was not as positive as usual and the winger's lack of flair was reflected in Birmingham's general performance.
The first half was a dire affair with neither side able to dominate.
Lomana LuaLua went close to giving Pompey a great start with a header which flew just wide from a Gary O'Neil cross, but that was the only occasion in the first period that City goalkeeper Maik Taylor was in any trouble.
Birmingham's goal attempts were little better. Stan Lazaridis twice tried his luck but neither effort was on target and Pompey shot-stopper Jamie Ashdown also had little work to do.
Fortunately the second half was much brighter as both teams displayed more urgency, as highlighted when O'Neil jinked his way inside only for Taylor to parry his low shot.
Seconds later Linvoy Primus cleared an Emile Heskey header off the line with Ashdown stranded.
Bruce was obviously far from happy with Birmingham's inability to break through Portsmouth's defence and made a double substitution, sending on Clinton Morrison and Julian Gray for Walter Pandiani and Lazaridis on the hour.
But there was no immediate improvement and Portsmouth hung on to gain a valuable away point despite some desperate attempts from Birmingham to break the stalemate.
Man of the match. Kenny Cunningham.
In a game dominated by the two defences Cunningham was the pick of the players on show. Diomansy Kamara and Lomana LuaLua rarely troubled the Irishman and Pompey were able to create few chances.