The Australia international joined the Hampshire club on a season-long loan in the summer to continue his development in the senior game across 2023/24.
Since then, he’s cemented himself in the current League One leaders’ side and has delivered a swathe of sparkling displays across 23 outings in all competitions.
For the Fratton Park chief, watching the 20-year-old’s development so far has provided immense satisfaction.
“If you take an overall view on it, he’s come into the side and proved himself as one of the first names on the team sheet every week,” Mousinho declared.
“[He’s] put in some really stellar performances over the past couple of weeks as well which has been a real positive.
“He’s been playing a position we knew he could play in, but one we didn’t necessarily bring him in to play. So now playing as one of our holding midfielders, one of our sixes, where he’s excelled – he’s been excellent.
“Overall, really pleased with everything he’s done so far. [He’s] established himself in the team, become one of our best players and for his first loan in this country he’s done really well.
“We knew he was going to have an impact, but we didn’t think he’d have the same impact he’s had. His progression has been upwards ever since he first set foot on the pitch.”
Following a strong start to the campaign, Portsmouth currently sit at League One’s summit - eight point clear of third-place Oxford United - as they aim to reach the Championship for the first time since 2012.
Although a 4-0 defeat to Blackpool in November, which ended a phenomenal 27-game unbeaten league run, threatened to derail their promotion bid – Mousinho’s men responded excellently by winning their next four successive league games.
The first of which was a professional 2-0 victory away at Burton Albion where Robertson netted his first senior goal.
After taking the lead at the Pirelli Stadium through Colby Bishop’s well-taken penalty, the Australia international doubled Pompey’s advantage when arriving into the box and coolly slotting into the bottom corner.
“I think the goal is big for him because the only criticism I would’ve had of him at this stage of the season is the fact he hasn’t converted all the excellent chances he’s had into goals,” Mousinho added.
“He’s had opportunities and he’s put himself into good areas and, to be honest, he’s been slightly unlucky in that goalkeepers have made some good saves.
“The pleasing thing about the Burton goal is he arrived in the box late and it made it a much easier chance for him whereas previously a lot of chances have come in and around the edge of the box.
“One thing we wanted to do with him, especially playing him deeper, is also encourage him to make the box. He has the athleticism and finishing ability – he wants to score goals.
“It was a big moment for him to get that first goal and quite rightly he fully deserved it and if we can turn him into a goalscoring midfielder as well who produces more than he’s currently doing then even better.”
Thanks to his productive spell at Fratton Park so far, Robertson has been exposed to the rigours of senior football consistently for the first time.
And Mousinho believes he can only benefit from challenges such as navigating the unrelenting League One schedule.
He continued: “We want to send a player back who has ticked all of the boxes.
“He’s travelled away with the first team, done the initiation song, got five bookings, scored a goal and had everything in between.
“You can only get that exposure if you’re playing first team football at league level.
“He’s done the lot. Played Saturday, Tuesday, Saturday and there’s been some adversity in there in losing games, but the highs of winning games as well.
“All of those things I think are really important for loan players to go back to football clubs with and say ‘that’s all done and dusted’.
“Hopefully [he can] slot into the first team and all those things that might be an obstacle for a young lad coming through the Academy, [he can say] ‘I’ve already done [that]’.
“I think that’s really valuable. Credit to Alex, with all those things, nothing has seemed too much for him and a lot of the time it can be.
“Going from the Under-21s side to the schedule which is brutal with 46 league games. We’ve played four EFL Trophy games, two league cups games and one FA Cup game already.
“That’s a massive adjustment and he’s adjusted to that really well.”
