Pompey have been hovering just outside the top six for a number of weeks now.
They briefly hauled their way in on Tuesday, only for Sunderland to win the following day and send them back out again.
But the Black Cats were beaten 2-0 at Fratton Park – thanks to goals from Christian Burgess and James Bolton – to send the hosts into the play-off positions.
The first half was as close as you would expect between two in-form sides, but Kenny Jackett was pleased to see his troops take control after the interval.
The Blues boss said: “Sunderland are an excellent side themselves, so to overcome them meant we had to play very well.
“There were many chances in the first half at both ends – I thought that they were as dangerous as we were. Both keepers had quite a bit to do.
"The division has been very open this season and there are some great sides in there, but I’m pleased that we’re in with a shout at the start of February."
“I was pleased with how we did after the break and we could have put a few more opportunities away.
“But we got the second goal and that was enough. It was a pleasing performance overall and we did very well.
“The division has been very open this season and there are some great sides in there, but I’m pleased that we’re in with a shout at the start of February.
“There are a lot of games coming up for us in three different competitions. It’s a big challenge, although one we should enjoy.”
John Marquis started the game leading the line for Pompey, but was replaced by Ellis Harrison at the break.
Jackett explained: “I just thought it was more a day for Ellis and he did prove to be quite a handful in that second period.
“The beauty of having both of those players in my squad is that there will be times for either of them and making a substitution can change the dynamic.”