Chelsea bounced back from Champions League defeat against Barcelona by extending their lead at the Premiership summit to 15 points.
Lampard celebrates putting Chelsea on the path to victory
Jose Mourinho's side had to wait 65 minutes to break down Portsmouth's resistance, but deserved the victory.
Frank Lampard swept home a right-foot finish from inside the area after good work by strike duo Didier Drogba and Eidur Gudjohnsen.
And Arjen Robben raced clear to add the second with 12 minutes remaining.
Chelsea made four changes from the side that was beaten by Barcelona - and Mourinho's re-shaped side dominated the first 45 minutes.
The recalled Shaun Wright-Phillips set the tone with an early shot that tested Pompey keeper Dean Kiely.
Chelsea made an intriguing tactical change after 31 minutes, taking off Asier del Horno and replacing him with Damien Duff, who went into an unaccustomed left-back role.
They stepped up the pressure, with Duff instantly setting up a half-chance for Wright-Phillips.
Kiely was emerging as Portsmouth's hero, blocking a close-range header from John Terry and saving well from Drogba's 30-yard free-kick as the interval approached.
And Pompey had another escape on the stroke of half-time as Wright-Phillips' cross flashed across the six-yard area with both Robben and Drogba unable to apply the final touch.
Chelsea continued to press and Kiely was in action again after 52 minutes with a double save from Wright-Phillips and Lampard.
Pompey had barely been seen as an attacking force, but it required a timely challenge from Robert Huth to halt Lomana LuaLua as he raced through.
Mourinho had watched with increasing frustration, and made a double change on the hour, replacing Wright-Phillips and Joe Cole with Gudjohnsen and Claude Makelele.
And Gudjohnsen was instrumental as Chelsea finally broke the deadlock after 65 minutes.
He cleverly dummied Drogba's pass and Lampard slid home a right-foot finish from just inside the area.
Portsmouth boss Harry Redknapp then sent on substitute Wayne Routledge as substitute, and he almost created an equaliser with a cross for Richard Hughes, who should have done better than head wide.
Gudjohnsen was the creator again as Chelsea wrapped up the points with 12 minutes left.
He lofted a clever ball through for Robben to race clear and beat Kiely with ease.
Chelsea assistant manager Steve Clarke:
"The Del Horno substitution was tactical and a ploy we have used before. I thought Damien Duff did very well at left back. He made a good contribution.
"When we made the double substitution it was to change the shape of the team as well.
"We took a risk, going three at the back and four up front, but when you bring on players of their quality you expect them to have an impact in the game. Thankfully for us that's what happened."
Portsmouth manager Harry Redknapp:
"It was no surprise Frank Lampard scored was it? Frank is always likely to score a goal.
"Up until that goal I never thought we were under real pressure but that's Frank. You give him one opportunity and he will take it.
"He broke into the box, which he is fantastic at doing.
"I didn't see Frank after the game but I will speak to him for sure. I love Frankie - he's not only a fantastic player but a fantastic young fellow.
"He is an absolute top-class role model for any young person in this country."
Chelsea: Cech, Paulo Ferreira, Huth, Terry, Del Horno (Duff 31), Wright-Phillips (Makelele 60), Joe Cole (Gudjohnsen 60), Essien, Lampard, Robben, Drogba.
Subs Not Used: Cudicini, Johnson.
Goals: Lampard 65, Robben 78.
Portsmouth: Kiely, Primus, Karadas, O'Brien, Taylor, O'Neil, Pedro Mendes, Hughes (Davis 72), Koroman (Routledge 68), LuaLua, Mwaruwari.
Subs Not Used: Ashdown, D'Alessandro, Todorov.
Ref: M Riley (W Yorkshire).