Pompey, who on Friday night became British football's largest fan-owned club after the Portsmouth Supporters' Trust took control, were dominant throughout.
And buoyed by the news the club will be docked 10 points for exiting administration this year and not, as feared, next season, Whittingham backed his side to end the campaign strongly and start next season - and a new era - in style.
He said: "It was a solid football performance from us. We did a good job and we were professional. We made sure we were solid and hard to beat and then we started to play football.
"We applied ourselves, we looked at Sheffield United's weaknesses and we tired to exploit them. We created chances and I'm obviously very pleased.
"We've got a group on the pitch now that people want to see back here next season. We've got one more game to go and we'll be looking to win that to build momentum for next season.
"But this win is our 'thank you' to the fans, plain and simple. They have stuck with us through thick and thin. The fans have never, ever stopped. This is for them."
After a scrappy start by both teams, Pompey took the lead after 21 minutes. Patrick Agyemang sent over a looping cross following good work by Jed Wallace on the right-wing which Shaun Cooper headed powerfully into the bottom left corner of the net.
The home side doubled their lead just three minutes later when Wallace fired a low ball into the six-yard box which David Connolly poked home from point-blank range.
And just after the half-hour Wallace got his name on the score sheet, side-footing home from eight yards out after a fine left-wing run and pull-back from Connolly.