Campbell opened the scoring for the Eagles before Gayle struck a hat-trick in the 4-1 win at Selhurst Parkin the third round of the league cup on Wednesday night.
After the game, Millen said: "It's nice to have your forwards scoring. Dwight and Fraizer looked sharp all night.
"They both looked dangerous so that will give everyone a confidence boost and it's nice to have some competition for the weekend."
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