Scott Parker scored his first goal for Chelsea as the Blues won a tough game.
Parker played a one-two with Adrian Mutu before shooting from short range but Pompey were unlucky not to equalise when Patrik Berger struck the post.
Yakubu shot over after a Neil Sullivan error before the striker forced a good save with an angled drive before Chelsea scored again.
Lampard's pass was lobbed against the crossbar by Jimmy Floyd Hasselbaink and Hernan Crespo chested home the rebound.
Chelsea went into the match with John Terry and Claude Makelele back in the team.
But Claudio Ranieri's team were again far from convincing against a Pompey side who denied them space and carried the fight to their expensively-assembled opposition.
Chelsea started well and opened up the Pompey defence with their crisp, intricate passing.
Jesper Gronkjaer received a deft return pass from Eidur Gudjohnsen but his cross-cum-shot flew wide of Shaka Hislop's goal.
Another one-two, this time involving Parker and Mutu, led to Chelsea's opener.
Parker laid the ball off to Mutu before bursting into space in the Pompey penalty area to collect the return pass.
The recent arrival from Charlton was then allowed far too much time by Pompey's static defence to control the ball before smashing home from seven yards.
Pompey rallied after conceding and were almost gifted an equaliser by Sullivan.
The goalkeeper smashed a terrible clearance straight at Eyal Berkovic and the ball broke to Yakubu, but the Nigeria international drilled his shot over from the edge of the area.
Nigel Quashie then went close before Berger smashed the Chelsea woodwork from long range with Sullivan stranded.
17 mins: Parker opens the scoring
31 mins: Berger hits the post
79 mins: Crespo scores with his chest
Sullivan saved from Yakubu close to half-time as Pompey continued to push forward.
Chelsea created the first good chance of the second half, Lampard bursting through the Pompey defence from midfield and forcing a decent save from Shaka Hislop.
But Pompey struggled to open up Chelsea and Harry Redknapp replaced Berger with Lomana LuaLua.
And the striker might have equalised from a Berkovic corner but made poor contact and his scuffed header drifted wide.
LuaLua went close from long range and a Berkovic free kick struck Lampard and deflected narrowly wide as Pompey pressed hard.
Chelsea substitute Hernan Crespo was booked for a terrible dive as Ranieri's team became increasingly desperate to make the game safe.
But the second goal eventually came with a move of supreme quality.
Lampard's raking pass picked out substitute Hasselbaink, who lobbed the ball over Hislop and against the woodwork.
Crespo, in acres of space, chested the ball home from 10 yards.
Portsmouth: Hislop, Primus, De Zeeuw, Pasanen, Stefanovic,
Quashie, Faye, Berger (LuaLua 56), Berkovic (Taylor 84),
Subs Not Used: Wapenaar, Curtis, Hughes.
Chelsea: Sullivan, Melchiot, Gallas, Terry, Bridge, Gronkjaer,
Parker (Cole 74), Lampard, Makelele, Mutu (Crespo 62),
Gudjohnsen (Hasselbaink 71).
Subs Not Used: Ambrosio, Huth.
Booked: Parker, Crespo.
Referee: G Poll (Hertfordshire).