Not since his strike against Middlesbrough ten games ago had the Ukrainian scored and the relief on his face when his left-foot strike hit the back of the net was evident for him and all the Chelsea supporters. His goal on 56 minutes was class.
Arjen Robben, always a threat, sent over a low left by-line cross and Shevchenko, running late into the Portsmouth penalty area, coolly slotted home across the path of David James and into the far corner.
Ballack's strike a minute later effectively killed the game off but James, in goal for Pompey, was the star, and prevented a Chelsea rout.
But it was the South Coast side, who started the better, and Kanu had an excellent chance on six minutes but he misdirected his header wide of Henrique Hilario's goal after outjumping Ricardo Carvalho on the edge of the six-yard box.
Chelsea responded three minutes later when Robben raced past Noe Pamarot and Didier Drogba volleyed the Dutchman's by-line cross over the Portsmouth crossbar.
James was called on to make two excellent saves within a minute. The first deflecting a shot by Robben and the second parrying away a powerful header by Shevchenko.
Chelsea had the ball in the Portsmouth net on 26 minutes when James punched the ball into his own goal. Referee Mark Clattenburg from County Durham adjudged that Drogba had fouled the former England goalkeeper.
Shevchenko brought the best out of James three minutes later as the striker darted into the Portsmouth area and produced a fine, curling right-footer only to see James miraculously dive high to his left to tip the ball around the post.
Robben and Ballack then had two attempts to break the deadlock, the first was saved by James, the second was sliced wide of the goal.
On 35 minutes, James again blocked a fine drive by Robben, this time with his feet.
On 39 minutes, Shevchenko became provider when his by-line cross was volleyed by Drogba into the ground and safely into the hands of James.
Again, Chelsea had the ball in the net when a James throw-out was intercepted. However, Robben passed for Shevchenko to put the ball in the net and was unfortunately offside.
James started the second half as he had the first, with a string of fine saves. On 48 minutes, a fine passing move from Chelsea saw Robben send over a left-wing cross which Frank Lampard firmly headed but the ball went inches wide of James' upright.
Chelsea's relentless pressure finally told with Shevchenko's strike on 56 minutes proving decisive.
A minute later Ballack's place in Chelsea history was assured with his goal.
Again, Robben decimated the Pompey defence, sending over a cross which Drogba headed back into the path of Ballack, who buried the ball past James with a fierce header.
However, both goal scorers were yellow-carded by Clattenburg for celebrating too close to the crowd.
Portsmouth rallied and almost grabbed a goal on 61 minutes but Gary O'Neil's diving header was well kept out by Hilario.
Eight minutes later Pompey got their rewards and scored when Benjani Mwaruwari bundled home a low right-footer into Chelsea's right-hand corner.
Chelsea could have restored their two goal lead, but James once again expertly smothered a blistering right-footer from Ballack.
Pompey couldn't get the equaliser and Chelsea safely saw the game to its conclusion.