Pompey needed a reaction following successive League One losses to Bristol Rovers and Blackpool.
And they certainly delivered at the Kassam Stadium, inflicting just a second third tier defeat of 2021 on in-form Oxford.
Harvey White grabbed the game’s only goal early in the second half by heading home a Callum Johnson delivery.
And Joe Gallen was pleased with a confident Blues performance that revitalised their promotion hopes.
Pompey’s assistant manager said: “The response from Saturday was exceptional. We played very well, looked organised and showed plenty of tenacity and intensity.
“We ran as hard as we have for a long time and were able to come up with a quality goal. The boys deserved their three points.
“Ronan Curtis looked bright alongside Ellis Harrison and we wanted to get behind Oxford, play with a physical fashion and cause some problems.
"We ran as hard as we have for a long time and were able to come up with a quality goal. The boys deserved their three points."
“They created some clear-cut chances from nowhere at the end, but there hadn’t been too many prior to that.
“Craig MacGillivray did well from a one-v-one and then a header and we were a bit disappointed to concede those opportunities.
“There are games coming all the time and it will be like that through to May. There isn’t a lot between the players in our squad.
“I know all of them well and they want to win desperately. They want to be successful and have a lot of character and belief.”
White’s winner came on his first start for the club and Gallen was pleased with how the loanee played.
He said: “Harvey looks young, but doesn’t play like that. We tucked him on the left side of midfield and were encouraging him to get into the box.
“He timed his run to perfection and it was a very good header into the net from a really impressive cross from Callum Johnson.
“The manager wanted to change things around and have a fresh energy and look about the team. He made some good calls.”