The former Newcastle forward made his Blues debut against Nigel Adkins' men 10 days ago, and netted twice in a 5-1 win at St Mary's
And the Senegalese forward has been chosen yet again for the Premier League meeting at Stamford Bridge, with Benitez making two changes from the west London outfit's 4-0 win over Stoke.
Branislav Ivanovic and Ryan Bertrand drop out of the starting line-up, with Gary Cahill and Oscar replacing them.
|BA'D LUCK, SAINTS
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Leading goalscorer Rickie Lambert drops to the bench with Gaston Ramirez, while Sean Davis and Guly Do Prado return to the side.
Chelsea: Cech; Azpilicueta, Cahill, David Luiz, Cole; Ramires, Lampard; Oscar, Mata, Hazard; Ba.
Subs: Turnbull, Ferreira, Ivanovic, Terry, Bertrand, Marin, Torres.
Southampton: Boruc; Clyne, Yoshida, Hooiveld, Shaw; S. Davis, Schneiderlin, Cork; Puncheon, Guly, Rodriguez.
Subs: K. Davis, Lambert, Ramirez, Fox, Ward-Prowse, Seaborne, Chaplow.