Pompey fans have been waiting a long time for a game of this magnitude - with League One's undoubted top two going head-to-head for the battle to be crowned the division's champions.
Five points separate the John Mousinho's table-toppers and the second-placed Rams who have played a game more. And although the Blues enjoy a healthy cushion over their nearest rivals, they'll be in no mood to go soft on their nearest challengers of the third-tier crown.
Indeed, the Fratton faithful want promotion and the league title wrapped up as soon as possible, with the champagne effectively on ice since that important win at Peterborough before the international break.
The outcome of tonight's game will go a long way to determining Pompey's fate, so Mousinho will want to get his team selection right for such a huge match. He's admitted two players from the Good Friday win at Wycombe are rated '50-50' for the visit of Derby, which is far from ideal whenever you have the likes of Regan Poole, Alex Robertson, Joe Morrell and Callum Lang unavailable through injury. However Pompey have performed superbly in their absence as the Blues' squad has stepped up to the plate to keep the chasing pack at bay.
There are signs of players coming back, too, with Lee Evans making his debut from the bench at Adams Park, while Tino Anjorin is in contention after a lengthy spell out with a hamstring injury. But can they break their way into the side for tonight's game? Or is the bench the best they and the ever-popular Kusini Yengi can hope for?
These are the dilemmas Mousinho must find the answers to. In the meantime, here's how we think Pompey will approach tonight's match...
1. Goalkeeper - Will Norris
The keeper was his usual reliable self last time out against Wycombe and could do little with Matt Butcher's goal. Will be a key figure in tonight's game against the Rams.
2. Right-back - Joe Rafferty
Rafferty found himself on the bench against Wycombe as Zak Swanson got the nod. The former Arsenal youngster did well, justfying the head coach's faith in him. Tonight, a huge test awaits against Corey Blackett-Taylor who seems to love playing against the Blues. Swanson's pace could prove handy, but Rafferty's experience could prove key to that battle.
3. Centre-back 1 - Sean Raggett
The central defender continued his impressive season with another strong performance at Wycombe. His experience, strength and aerial ability will be key tonight, especially id James Collins starts.
4. Centre-back 2 - Conor Shaughnessy
Pompey's 'find of the summer' has another huge test on his hands tonight. But Shaughnessy has proven all season that he's more than capable to silencing the best strikers in the division. Photo: Jason Brown