Pompey are now seven points adrift of the top three following Saturday’s 1-0 defeat at the hands of Oxford United.
Substitute Jordan Bowery settled the Fratton Park contest with a sweet first-time strike on 76 minutes.
Michael Appleton’s side also saw Liam Sercombe’s penalty saved by debutant Ryan Fulton, while at the other end Jake Wright cleared a Marc McNulty shot off the line.
Crucially for the U’s it increases the gap to fifth-placed Pompey, although Paul Cook’s men have games in hand on the teams above.
In addition, they are now 14 points behind current leaders Northampton, who the Blues beat in December.
Yet with 20 games to play, Close believes nobody should be panicking.
The midfielder said: ‘It might seem like a big defeat but there are plenty of games to go.
‘There are a lot of matches to play for, a lot of points to play for and we are going to keep pushing and try to win as many games as we can until the end of the season.
‘The next league game is at Morecambe and we will try to win there, there are plenty of points to play for and make that first place ours.
‘On Saturday there was disappointment in the dressing room. We had just lost to contenders for the title, but are not going to get too down, we have games coming up in the FA Cup and league and will keep our heads up.
‘The points difference might seem a lot now but teams lose, especially at this stage of the season.
‘Teams might get nervous, fitness might come into consideration and we are a fit team, have a good squad and I feel confident we can still make it.
‘Maybe we didn’t deserve to beat Oxford but if we can keep our good form up I am confident we can still beat a lot of the opposition in our remaining games.
‘We weren’t quite at it in the first half, to be honest I didn’t think either term deserved to win, neither team created chances, but we have got to take it on the chin and move to the next game.
‘It was a tight game. They had a penalty, we had a good chance in the first half, scrambles late on but to win games you have to create more chances than we did.’
Close appeared as a 55th-minute substitute for Adam Barton in Saturday’s defeat.
It represented a first league appearance of the campaign, although he has made four starts in cup competitions this season, most recently at Ipswich.
The 19-year-old from Fratton impressed during an improved second-half display from the hosts.
And he was delighted to be part of the action.
He added: ‘It was disappointing to concede the goal and lose the game but great to get 35 minutes under my belt and hopefully I can get some more minutes from now until the end of the season.
‘I felt good out there. Obviously fitness isn’t an issue with only 35 minutes to play, but I was trying to keep the game ticking and get us going forward, attempting to unlock the back door.’