Forget the seven-year age difference - and the £29million difference in transfer fee - both strikers are being brought to their new clubs for the same reason.
Lambert, a direct and experienced target-man has been recruited by Brendan Rodgers because he offers something different - a plan B and an ability to break down stubborn defences.
An inability to score against a disciplined, defensively resilient side struck Liverpool twice last season - against Southampton and Chelsea, both at Anfield. With the Reds missing out on the Premier League title by three points, a sufficient outlet in either of those games could have proved crucial.
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Rodgers' side also scored just once in each of their opening three games (when Luis Suarez was suspended), although Liverpool won on all three occasions. A failure to take more chances against West Bromwich Albion and Hull City did cost them, however.
There are not many examples, of course, as the Reds tended to outscore most of their opponents throughout the league campaign. Lambert's arrival, though, has still been deemed necessary based on those fine margins.
So, for a Chelsea side that had less of a problem keeping clean-sheets but a huge problem scoring goals, you can understand why similar thinking could be being deployed.
At 25 and after a prolific season for Atletico Madrid, the signing of Spain striker Costa is a move that makes sense for many reasons. It is his style, though, that may make him the ideal solution for the Blues' goal-scoring woes.
Remarkably, Chelsea went goalless on eight separate occasions during last year's Premier League campaign, scoring just once during a further seven.
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A majority of those came against sides visibly happy to play for a draw - Norwich City and the side Jose Mourinho accused of playing "19th century football" West Ham, for instance. Others hit the Blues with a sucker punch and defended astutely for the rest of the game - Aston Villa and Everton two such examples.
The solution Mourinho appears to have chosen is a strong, direct aerial threat who could offer Chelsea a simpler, more effective option in Costa. The likes of Eden Hazard, Oscar, Willian and more are adept at keeping the ball on the ground and trying to weave their way through defences - but sometimes that approach just doesn't cut it. Just ask Didier Drogba.
For the same reason that Lambert has been brought to Anfield, then, 25-year-old Costa will be the man entrusted to give the Blues a greater attacking edge. Both will be key for their sides this season in tight, tactical affairs, while they will be equally crucial from set-pieces and crosses.
The main difference? Costa will likely start week in, week out, whereas England man Lambert will have more freedom and less responsibility. And with the money involved in bringing Costa to west London, that means a whole load of extra pressure on the Spaniard to deliver.