It was all smiles when Pompey trooped down the Oakwell tunnel after as dominant a first half display as you could hope to see.
Goals from Colby Bishop and Paddy Lane – both on eight minutes – preceded a Connor Ogilvie header that left the visitors with a commanding lead at Barnsley.
But their hosts hit back after the interval, with Barry Cotter and Callum Styles ensuring there was as much a sense of relief as there was delight when the final whistle signalled a 3-2 victory.
John Mousinho was delighted with how his table-topping side started the contest, but admitted they could have been better in the second half.
The Blues boss said: “That was probably the best 45 minutes I’ve seen since I arrived here and that was reflected in the scoreline.
“We thoroughly deserved to have the lead we did at the break and it could have been four or five goals for us.
“If we’d have got one more then I think puts the game to bed and just calms everything down, but you can’t have everything.
“We pressed really aggressively high up the pitch and just made good decisions – some of the bravery and the ability to break the lines was just a joy to see.
"The second half was absolutely awful – it went from the best 45 minutes of my time here to the worst!"
“There wasn’t a huge amount I could say to the players at half-time, other than be ready to adapt because Barnsley will change.
“But the second half was absolutely awful – it went from the best 45 minutes of my time here to the worst!
“It was a culmination of things, with Barnsley changing their system, us starting to make poor decisions and not track runners.
“That energy wasn’t quite there, but we can put that down to the amount of travel we’ve had, coming here after going to Derby at the weekend.
“It was a case of us having to dig in, but we saw the game out well and didn’t concede too many chances at the end.”
Christian Saydee was missing for the second game running, while Sean Raggett and Zak Swanson were also absent from the squad in South Yorkshire.
Mousinho said: “Zak had a family issue that he had to deal with, otherwise he would have been in the squad. There are some things that are more important than football.
“We weren’t quite happy with Christian being able to play and it’s a case of us managing that because we don’t want him to break down.
“Raggs was struggling with a foot problem in the warm-up on Saturday, so we thought it was the right decision for him to rest up.”