Jackett changed formation for the visit to the Galpharm Stadium, switching to a five-man midfield that meant the Alexander, who has only just returned from injury, was an isolated figure for most of the afternoon but repaid his manager's faith with a fine performance.
"He's a handful for anybody," said Jackett after the game. "I was very pleased for him and was unlucky with his chance. It helped the wingers to play higher and the plan was Martin and Henry to play as front three.
"We had the lion's share of the play in the first half and gave them a lot of problems in the first half. We got in a lot of good crosses but couldn't get on the end of them."
The Millwall manager was also quick to praise substitute Scott Barron, who set up the winner for James Henry.
"A terrific run and an excellent final ball at the end of it. He's pulled it across goal and Henry was there to finish."