Palace won 2-0 at The Hawthorns on Saturday afternoon to move three points clear of the relegation zone, thanks to goals from Wilfried Zaha and Andros Townsend, and Sakho was impressive throughout.
The defender, who is on loan from Liverpool, has now helped Palace record successive clean sheets since arriving at Selhurst Park.
Palace finally appear to be putting their defensive woes behind them and Allardyce said of the Frenchman: “The lift he has given us defensively in the two games he has played has been exceptionally good.
“You are slightly concerned when you take a player who has been frozen out in the January window.
"But then again, once we have got him fit - and we got him fit quick with the way he applied himself.
"You don’t play that many games for Liverpool if you are a bad player,” he added.