Hat-trick hero Benjani and £5million new signing Lassana Diarra vindicated Portsmouth manager Harry Redknapp's decision to reject the overtures of Newcastle as a six-match goal drought was finally ended at Fratton Park.
After going behind in four minutes Benjani scored his second treble of the season - including Pompey's first home league goal since September 29 - while Frenchman Diarra produced a debut performance of exciting promise.
The hosts were no better than seemingly-doomed Derby for half and hour but Benjani's talents gradually gave them the edge and victory was already a formality by the time he completed his hat-trick with a spectacular virtuoso effort after 54 minutes.
'I want them to play like that. They are good footballers and I want my players to play and that's why I bring them here,' said Redknapp.
'I said to to Benjani that we needed a big performance from him because we are missing the African Nations Cup boys (Sulley Muntari, Kanu, John Utaka and Papa Bouba Diop) and he did the business.
'I still want to get an extra front man. I think the squad needs another front man, because we are short but they are not easy to find.
'But you have to balance the books, you just can't expect them (the club) to keep pulling up money.'
Redknapp, who raised the cash for Diarra by selling Matt Taylor to Bolton, was delighted with his debutant's performance and expects him to get better.
'He is a top player so to have him here, with Muntari, Diop and Utaka we will look quite strong,' he added.
Zimbabwe striker Benjani, whose country failed to qualify for the African Nations Cup, now has 12 goals for the season.
'It is a special feeling for a striker to get a hat-trick and even though I was substituted just before the end I came back onto the pitch again to make sure I got the match ball,' he said.
Diarra, who could not hold down a regular place at either Chelsea or Arsenal despite playing nine of the last 10 France internationals, insisted the best is yet to come from him.
'I know a lot of players here and that's why I signed, but also because I knew the manager wanted me,' said the 22-year-old.
'It helps my mind to know that I am going to play [nearly all] the games with Pompey and I know I can do better because I only trained once with my new team-mates and had not played at all for four weeks.'
Diarra had been accused of merely using Pompey as a stepping stone back to a big club but he denied this.
'I'm here to win things and refocus my football. I think Europe is realistic for us with the players we have - especially when the African players come back,' he added.
The midfielder was lucky to avoid a yellow card, at least, for a late first-minute lunge on Derby defender Darren Moore.
Minutes later David James palmed Emanuel Villa's header onto the crossbar after a free-kick by ex-Pompey player Laurent Robert but Wales youngster Lewin Nyatanga was on hand to slot home the rebound.
Kenny Miller missed a chance to make it 2-0 - James saving bravely at his feet - before Benjani eventually equalised with a shot on the turn before heading his side in front.
Fellow striker David Nugent made vital contributions to both goals but Benjani's third nine minutes after half-time was practically all his own work.
Surging out of his own half, he swapped precise passes with Pedro Mendes, and clipped a lovely drive beyond Lewis Price.
Paul Jewell, who saved Wigan from relegation on the final day of last season, all-but accepted the battle for survival was over after going 18 matches without a win.
'It's not easy to stand here and say we are down but I am a realist,' he said.
'Next season I want players who are going to get us back up to the Premier League and when you see the plans the chairman has, it can happen.
'Some teams that go down might not be seen again in the Premier League but I don't believe Derby is one of them.'