Chelsea coach Carlo Ancelotti praised midfielder Frank Lampard after he earned the Blues three valuable points with a second-half penalty.
Lampard, who missed his last penalty against Manchester City, kept his concentration to score from the spot after Branislav Ivanovic had been fouled by Marc Wilson.
Nicolas Anelka had given the Blues a first-half lead only for Frederic Piquionne to level five minutes after the re-start.
But Lampard's winner also ruined the return of former Chelsea boss Avram Grant. The Israeli was back at Stamford Bridge for the first time since he was sacked in the summer of 2008.
"I have trust in Frank because he shoots penalties very well," said Ancelotti. "He missed a penalty at Manchester City but he's the best penalty taker for us.
"It was a very good penalty tonight because it was not easy. There was a lot of pressure on that penalty. He did very well."
But Ancelotti also accepted that Chelsea once again lost their way again once Pompey had levelled.
"We lost our composure for 15 minutes and, for that period, it was difficult," added the Italian. "But we deserved to win the game. I don't know why we're losing that composure.
"After four games without a victory, and when Portsmouth equalised, we didn't have confidence that we would win the game.
"Probably that was because we didn't win in the last four games. It is a moment - it was important to return to winning ways. We did that. We did a good job, not a beautiful job.
"I'm happy because it was becoming a difficult game after they'd equalised. We had 15 minutes in the second half which were no good. We lost our composure.
"But, then, we had a very good reaction. We changed something on the pitch, put fresh players on, and had a very good reaction until the end of the game.
"We deserved to win, but that was the most important thing after four games without a victory. The first aim was always to win.
"The players are not suffering from nerves, no. They are not nervous. In this case, we can do better. We have a lot of players with strong personalities. Communication in this case is the most important thing."
Pompey remain rooted to the foot of the Barclays Premier but coach Grant was pleased with the performance of his side.
"We played well," said Grant. "We played against a team who are very strong at home.
"But they didn't create many chances and in the second half we had two big chances. But they scored a goal from no chance really. The result is disappointing but the performance was good.
"Of course it was a penalty. Marc is a very good young player but sometimes inexperience costs. He made a mistake but he is a very good player. It was a pity because I could not see how Chelsea would score."
Grant was also touched by the reception from Chelsea fans who still recognise his efforts in taking the club to their only Champions League cup final in 2008.
"It was touching," he added. "It was a great year and the reception made my heart warm."