Pompey's 2-1 defeat over Wigan Athletic on Monday set up another pivotal clash this weekend in their hunt for the play-offs.
Kenny Jackett's troops travel to struggling Rochdale tomorrow, who sit 23rd in League One and four points from safety.
A win for either side would keep the pressure on the teams above them.
Here's all you need to know about the Dale ahead of the clash...
The gruff Keith Hill is a Rochdale legend having more than 15 appearances for the club in his playing days, while taking charge of more than 500 games across two spells as boss.
After holding the reins as caretaker manager, Hill permanently took the Spotland hotseat in January 2007.
His affect from the time as caretaker to the end of that season was substantial as he took Rochdale from the League Two relegation zone into the top 10.
What followed were two seasons of play-off heartbreak before the club gained automatic promotion in 2010.
For the first time since 1974, Rochdale were out of the fourth tier.
Hill, who admits to watching Monday Night Football to learn and improve as a boss, led the Dale a ninth-place finish the following campaign in League One.
His success at Spotland attracted interest from Barnsley. However, Hill lasted less than two seasons at Oakwell despite keeping the club in the Championship.
He returned to Rochdale in 2013 and led the club back to League One - where they have been since.
One to watch
Pompey will need to be wary of the crafty forward play of Ian Henderson.
The veteran attacker is not an out-and-out striker despite leading the club's scoring charts with 17 goals in all competitions.
Henderson is keen to drop off and be involved in play, while also trying to produce the finishing touch to a move.
The 33-year-old ranks in the top-15 in League One for shots, headed shots and through passes and he has had a tendency to score doubles, netting four this season.
Rochdale have lined up in a number of formations this season but in recent weeks Hill has settled on a back five which can easily become a back three. Since the switch they have kept six clean sheets in their past 11 games.
Despite enjoying the division's highest amount of percentage they don't pass for the sake of passing.
Out of possession they like to compete. No team has had as many defensive duels, while only Gillingham and Rotherham have committed more fouls.
Brett Pitman's debut double inspired Pompey to a 2-0 victory over the Dale in their League One curtain-raiser.
Dale were hampered by a Keith Keane red card after 21 minutes, with both goals coming after the break.
The Blues also went down to 10 men when Jamal Lowe was sent off.
Postponements and FA Cup priorities haven't helped Keith Hill's side find a measure of consistency.
Since losing to Tottenham Hotspur in an FA Cup replay Dale have only lost once in the league in seven encounters.
They have two, three and four games in hand over teams above them.
Surprisingly, Rochdale have recorded the highest percentage of possession in the league, enjoying 52.5 per cent of the ball, ahead of Shrewsbury Town, Charlton Athletic and Pompey.