Kenny Jackett is looking to avoid a Carabao Cup hangover this weekend.
Pompey suffered their first defeat of the season against AFC Wimbledon, which followed back-to-back League One wins over Luton and Blackpool.
Jackett does not regret making changes to his side against the Dons, especially with a hectic run of matches coming up.
But he wants to see his players come bursting out of the traps when they take on Oxford at Fratton Park on Saturday.
The Blues boss said: “All five of the switches we made are players who I believe are genuine contenders that we will need over the course of the season.
“Managers usually make a number of changes at this stage of the competition – and it’s mostly down to the volume of games.
"It’s important that we start well against Oxford on Saturday and establish ourselves."
“You need a group that’s strong enough and it was nip-and-tuck and a tight contest that just went the wrong way for us.
“So after a poor ending it’s important that we start well against Oxford on Saturday and establish ourselves.
“We’re looking to continue our positive form in the league in a fixture that will certainly be a test for us.
“My focus is on trying to play on the front foot and work as hard as we can to get into the game right from the start.”
Pompey will face an Oxford side who recovered from successive league defeats to beat Coventry in the cup.
Jackett said: “They have a good squad and also a good manager. The players that have been added in complement what is already a competent group.
“I don’t know why it didn’t quite happen for them last season, but they’ll obviously be looking to be nearer the top this time around.
“Looking at the quality and strength in depth Oxford have, I do believe they are one of the sides that can challenge.”
Jackett will be without the injured duo of Dion Donohue (groin) and Nathan Thompson (knee) against United.
He explained: “Both are progressing well, but won’t be fit for this game. We hope to have them back at some stage next week.”