Hirst has been a revelation over the second half of the season, with fans clamouring for his signature after bagging 12 goals to date.
They’ve all arrived since November, with the 23-year-old enduring a tough start after failing to score in his first 13 games.
That changed on an unheralded November evening against Crystal Palace under-21s in the Papa John’s Trophy, as Hirst bagged a stoppage-time goal in the 3-0 win.
Robertson can see what that moment did for the striker and his confidence, paving the way for what followed.
He said: ‘George has been on fire, absolute fire.
‘I thought his Rotherham performance was one of his best of the season.
‘It’s just confidence for him.
‘Since he came into the team against Crystal Palace in the Papa John’s Trophy it’s been different for him.
‘Since then he’s really kicked on.
‘It’s just confidence and playing every week which has made the difference.
‘It’s confidence and getting into good positions.
‘His hold-up play has been very good and important for us.
‘I’d take him back here next season.
‘I’d definitely like that, he’s a great boy, everyone in the dressing room likes him and he’s a pleasure to work with.’
Hirst came into this season at Pompey off the back of a tough campaign at Rotherham, where he failed to score in 32 appearances.
Just how far he’s come since was underlined as he scored a goal and grabbed an assist against the Millers at Fratton Park, in the 3-0 win last week.
Robertson added: ‘He had a hard time at Rotherham.
‘To be fair, he didn’t start many games there.
‘It was always 10 or 15 minutes coming off the bench at the end.
‘It’s always difficult coming on as a sub when you’re chasing games to make an impact.
‘Since October time when he came in, though, he’s been excellent.’