Ba enjoyed a prolific 18-month spell with the Magpies, scoring 29 goals in 54 Premier League appearances, but he angered many Toon fans by leaving the club at their lowest point to join the Blues.
Given Fernando Torres' latest poor showing in front of goal against Reading on Wednesday, Ba looks almost certain to be recalled to the starting line-up this weekend and Azpilicueta is sure the Senegalese will have his mind on the task in hand.
The Chelsea defender said: "I don't know how they (Newcastle fans) feel. Demba is a Chelsea player. He's going to do his best for Chelsea. It's true that he played very well there so I think they must be disappointed because he's a very good player, but he's going to be focused on the game."
Chelsea threw away a two-goal lead against the relegation-threatened Royals in midweek to emerge with only a point from the Madejski Stadium.
Sloppy marking allowed Adam Le Fondre to pounce twice in the final eight minutes after Frank Lampard and Juan Mata had given the visitors a seemingly comfortable lead.
Interim manager Rafael Benitez is expected to confirm today whether Mata will be fit to take on Alan Pardew's side.
The Spanish international hobbled off towards the end of the game at Reading with an ankle problem.