Brandon Haunstrup was left wondering what might have been after Pompey were beaten in the south coast derby.
They had a number of opportunities to break the deadlock in an frantic Carabao Cup third round tie at Fratton Park.
But Southampton showcased more of a ruthless edge, with Danny Ings’ brace and goals from Cedric and Nathan Redmond.
And Haunstrup was left frustrated that they did not have anything to show for their early dominance.
The defender said: “You look at the result and see 4-0, but in the first half we gave them a really good game.
“We just didn’t take those chances and you need to do that against Premier League opposition because it’s hard to sustain that level of performance.
“I felt like a goal was coming for us and we could have been one or two up. Then it might have been a different story.
"We just didn’t take those chances and you need to do that against Premier League opposition."
“But that’s how football goes and we needed to be more clinical because it was a disappointing evening.
“We know that we need to cut out the sloppiness at the back and take those opportunities at the other end.”
Fratton Park was packed for the latest contest between fierce south coast rivals and Haunstrup was impressed with the atmosphere.
He said: “It’s a game I really wanted to be involved in, so we’re gutted at the result, but seeing how the fans were with us at the final whistle was unreal.
“They gave everything for us for the full 90 minutes and it was unfortunate that we couldn’t pay them back.”