Ba enjoyed a prolific 18-month spell with the Magpies, scoring 29 goals in 54 Barclays Premier League appearances, but he then 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.
Mata said afterwards: "There are no excuses. I don't know (if the collapse was down to a lack of belief), but it can't happen again.
"This match was very important because we had an opportunity to be closer to Manchester City and make the gap even bigger to the teams in fourth, fifth and sixth place but we didn't manage the game way we should have."
Interim manager Rafael Benitez is expected to confirm on Friday whether Mata will be fit to take on Alan Pardew's side. The Spain international, who has been in excellent form for the Blues this term, hobbled off towards the end of the game at Reading with an ankle problem.