Zlatan Ibrahimovic, Neymar Jr. and Kylian Mbappé have all delighted and dazzled for PSG, but it could be argued that the best value for money signing - and arguably the most transformative buy of them all - has come at the other end of the pitch.
Keylor Navas cost Paris Saint-Germain just 15m euros when he joined from Real Madrid in 2019. Through his brilliance on the line and, above all, his calm, reassuring presence, the Costa Rican goalkeeper has helped the French champions take an important step forwards.
"I really feel that here I have the trust of my teammates, of the club, and of Leonardo, our sporting director who showed faith in me by deciding to bring me here," Navas told the Ligue 1 Show on beIN SPORTS.
"When I arrived, he said he was counting on me to repay that faith. Leo gave me this opportunity. He said 'come and sign the contract here, come and work with us. I believe in you'. Then I met a group of teammates who also believed in me. That's very important. I have a big responsibility here. But that's something I like."
Since Navas's super-human performance against Barcelona in the UEFA Champions League on 10 March, when he made nine saves - including one from a Lionel Messi penalty. -he's been thrust into the media spotlight.
His face has been splashed across the front pages and his appreciative teammates are now hailing him as a game-changer. At last, aged 34, the goalkeeper who had a relatively low profile in Madrid, is getting the recognition he deserves.
"I just try to do my best," he continued. "I do everything I can to help the team to win, and I try to give my teammates confidence. I strive to make sure that I do my job well. I like the fact that my teammates feel this trust towards me, because it's something I look to transmit out on the pitch. They need to know that they can rely on me.
"And I always look to thank them for the support they give me, because I'm not playing games on my own. We have 11 subs who can all step into the team if need be. And you only win games through a collective effort. Having mates who truly value you and the work you do is nice feeling."
Navas's principal attribute is his coolness. No matter how tense the occasion, or how difficult the game, the goalkeeper remains level-headed throughout.
"Thanks to God, I have this very calm personality," he explained. "I never get too down during the difficult times, and I don't get carried away in the good times either. I try to remain very calm and consistent. When I'm focussing on a match - when I'm about to walk out onto the pitch - I think 'I want to win' no matter who we're playing. Regardless of the opposition, if you want to win, you have to respect them, and then make sure you do better than them. That's what I try to do in every game."
The secret to his success is simple…
"You have to work hard," Navas stated, "I think work is the key to everything. Regardless of how much talent you have, it's so important to work and put in the effort to ensure you go into the games in the best possible condition. If you do that you'll rise to the occasion.
"I don't want to go into training in a bad mood. That's not what I like. I like to enjoy my work, to laugh and talk with my teammates, to try to stop every ball that comes my way. That's part of my life and it's what I enjoy doing.
"I always say that playing a football match is like sitting an exam at university. If you do your revision, when you go into the exam you'll feel ready for it. Likewise if you train well all week, really work hard, then when the game comes around you'll feel confident and you'll do things well. That's what I try to do, to ensure that I go into the game with confidence, then I can enjoy it. I think you can improve every single day. I always want to learn. I try to learn from all the other goalkeepers and all the coaches, because that helps me to be as good as I can, and I want to get better every day."
If Navas is still improving it's bad news for the attackers he faces. This season he has kept out more than 80 per cent of the shots he's faced, making him Europe's most effective goalkeeper ahead of Atletico Madrid's Jan Oblak, Chelsea's former Stade de Reims and Stade Rennais FC man Édouard Mendy, as well as Manuel Neuer of European champions Bayern Munich.
"For me, the most important thing is to make sure I feel ready mentally," Navas explained. "Whether to rush off your line, or hold your position, these are decisions you have to make quickly. But if you've worked on it a lot in training already, it really helps, and it becomes natural."
But can the French league's leading custodian tell us about his favourite save?
"Hmm. I remember the most recent ones. I like penalties. I enjoy it when I save a penalty. I also remember saving a header that came to me quickly. There was a shot at Nice, it was a cross-shot. I really had to reach to for it. That was good. I remember that one, it happened quickly. But I like every save because every save is important."
Mauricio Pochettino would surely prefer it if Navas had less work to do. But it hasn't been an easy season for the French champions, who have already lost seven times in Ligue 1 Uber Eats, and now face an almighty battle with LOSC, Olympique Lyonnais and AS Monaco for the title.
Watch: PSG were edged by LOSC in their most recent league outing
"We don't like to look for excuses," said Navas. "But I don't think it's a secret that this season has been an unusual one for all of the teams. We got to the final of last season's Champions League, and whilst we were playing in that final, the new season was already commencing in France. We only had a one-week holiday, and I think that's probably cost us in the long run, because it just isn't the same as having a proper break and a proper pre-season to prepare, to work together to prepare the team."
PSG also have competition this season because their rivals have improved significantly. Lyon put Navas and friends to the sword at the Parc des Princes, while Monaco have beaten PSG twice this term. The capital club are hoping the most recent defeat by LOSC doesn't prove to be decisive.
"In these moments you have to give absolutely everything, " Navas continued. "As a footballer, you're very fortunate to play in these matches. They're the big games, the kind of games everyone wants to play in.
"I think it is a different league this season. The other teams have improved. There's more strength now, and things are much closer at the top. We need to approach the final games in a very professional way, and we have to win them! We don't have any other choice now. That's the only way we are going to win the title."
If Navas has already won domestic titles in Costa Rica, Spain and France, he also knows what it takes to win the Champions League, having lifted Old Big Ears three consecutive times with Real Madrid.
Now he wants to help Paris claim their maiden crown, and, despite drawing the holders Bayern in the quarter-finals, Navas is convinced the French club can go all the way, especially after winning the first leg of their quarter-final 3-2.
"I always believe we can win it," he concluded. "I don't think any player in the world plays the Champions League thinking they are going to lose. If you think like that you might as well stay at home. I believe you have to go into the games with this winning mentality, and with humility because we are up against a great team. But we have to have confidence in ourselves because we have a lot of top players who are capable to winning this trophy.
"We're not far off. We have to enjoy every moment, fight for everything, and put our hearts into every single action."