Kenny Jackett came to Pompey with plenty of pedigree, having previously led Swansea, Millwall and Wolves to promotion.
But his last managerial role before arriving at Fratton Park was a 39-day stint at Rotherham.
He leads his new side into battle against his old one in a game being televised live on Sky Sports on Sunday (2.30pm kick-off).
Jackett admits he made the wrong decision to take charge of the Millers, but is now fully focused on guiding Pompey to success.
The Blues boss said: “It was a brief stint. I read the situation wrong and obviously it closed rather quickly, but sometimes it’s the best thing for everyone.
"I’m working hard to make sure we build a successful team that can be strong in League One."
“I’ve moved on to Pompey and it’s a job that I’m committed to. I’m working hard to make sure we build a successful team that can be strong in League One.
“We’re looking forward to the game on Sunday and it should be a good occasion in front of the Sky Sports cameras.
“Rotherham have come down from the Championship and have had quite a high turnover of players since the summer.
“But there are some big threats in their side and some of their results so far have been a bit unlucky.
“It’s still very early days and I’m sure they’ll be working hard to get the right equation and find the best team.”
Nathan Thompson could replace the suspended Gareth Evans at right-back after recovering from the foot injury that has kept him sidelined since pre-season.
Jackett said: “Nathan has worked hard in training and I’ve been very pleased with him. He’ll want to prove himself and build his match fitness.
“He’s a versatile player and you need that in your squad, particularly with the injuries we’ve had to defenders this season.
“Matt Clarke’s back in training and we’ll have to see whether it’s right for him to be involved in Sunday, but Drew Talbot is probably a week away.”
There could also be debuts for Damien McCrory, Stuart O’Keefe, Matty Kennedy and Oliver Hawkins after the quartet signed on Thursday.
Jackett said: “It was a busy deadline day, but we were really pleased with the business that we were able to complete.”
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