Midfielder Frank Lampard insists Chelsea can fend off any new year title push from Manchester United.
Chelsea overcame a spirited performance from Avram Grant's side thanks to a 79th-minute spot-kick from Lampard.
The former Chelsea boss looked to have heaped more misery on the Blues, who had taken only one point from their previous two games, when Pompey striker Frederic Piquionne cancelled out Nicolas Anelka's first-half opener in the 51st minute.
But Branislav Ivanovic was felled by the inexperienced Marc Wilson and Lampard, who missed his last penalty in the defeat at Manchester City, scored with ease.
Chelsea remain three points clear at the top but United boss Sir Alex Ferguson believes his side will emerge triumphant in the title race because they are traditionally stronger after Christmas. Lampard, however, disagrees.
"United have a history of doing it but we've had a history of doing it as well," declared Lampard. "We're very determined.
"We had a really bad time around this time last year but when Guus Hiddink came in we were in the best form by far of anyone in the league. We can do that again."
But Chelsea will have to undertake more work on set-pieces after conceding from a dead-ball situation yet again against Portsmouth.
It is an area Lampard accepts needs to be addressed sooner rather than later, with 12 of the 14 goals conceded by Carlo Ancelotti's side coming from set-plays.
"We're having a patch at the moment where we're not pulling away from teams when we might do and every free-kick and corner seems to drop to them in a funny way," added Lampard.
"We are being punished every time and it is just a phase we're in. We're going 1-0 up and then not pushing on like we were a few games ago. It's a problem at the moment.
"We have to be a bit more careful when the ball is in our half even if the opposition are playing a bit deep because teams like Portsmouth can load players into the box at free-kicks.
"It's important to try and stay on your feet. Some fouls you can't help because you've mistimed the tackle but we don't want to be too clumsy and let people keep launching it in the box."
Chelsea now face Lampard's former club West Ham on Sunday and he is convinced ex-Blues duo Gianfranco Zola and Steve Clarke can save the Hammers from the drop.
Lampard has been jeered by West Ham fans every time he has returned to Upton Park following his £11million move to Chelsea in 2001.
But he is not gloating about their plight near the foot of the Barclays Premier League.
"It's difficult for West Ham at the moment," he said. "They have a lot of financial difficulties and have had to sell a lot of players.
"I have a lot of respect for Gianfranco and Clarkey and I don't want to see them do badly at all. They're great lads. It's difficult but then it's a difficult league."
Portsmouth striker Piquionne marked his return to the Pompey side with a goal and the on-loan Frenchman believes, if they continue to perform at the same level, Grant's side can escape relegation from the top flight.
"I think and I hope we have shown we can stay up, because that is what I've come into this club for," said Piquionne.
"I know the situation is difficult but, if we play like we did at Chelsea, I think that we have enough quality to stay up. Hopefully things will be better in the next game now."
Piquionne, on loan from Lyon, gave Chelsea captain John Terry and his defensive partner Alex a torrid evening despite playing much of the game as a lone striker.
His goal arrived courtesy of Chelsea's inability to defend Jamie O'Hara's free-kick, and he added: "I was happy. It has been a long time since I played like that. But I was given an opportunity and I think that I did a good job.
"Chelsea are not well at the moment and I think we were unlucky. We had a lot of chances but maybe the last pass was not good. They are a good team, a strong team and we have worked them hard."
Lampard: Blues won't crumble | ESPNSTAR.com
