Reshmin Chowdhury is a TV sports broadcaster covering the Champions League and will be writing for the BBC Sport website during the competition.

Love was in the air at the Parc de Princes on a cold Valentine's night in Paris two years ago. The cheer at full-time was deafening. I'm not sure many would have predicted a scoreline as one-sided as this. This was big.

Paris St-Germain had just beaten Barcelona - THAT Barcelona - 4-0 at home in the first leg of the last 16 of the Champions League.

I was standing in the tunnel ready for my post-match interviews, watching some of the greatest players of their generation walk past, heads down, humiliated. The likes of Lionel Messi, Andres Iniesta, Neymar and co couldn't get away fast enough.

I spoke to goalscorer Angel di Maria and then boss Unai Emery after the game. Di Maria was humble, but quietly confident. Emery warned that the tie was far from over.

Paris St-Germain celebrate their 4-0 first-leg victory over Barcelona in February 2017

And so it proved. That night in Paris was as good as it got for PSG, as their dreams of European glory came to a cruel and soul-destroying end just three weeks later.

I don't think they've ever recovered.

Barcelona achieved mission impossible, becoming the first team to overturn a 4-0 first-leg deficit in the competition, winning 6-1 to knock the French side out 6-5 on aggregate on an unforgettable night at the Nou Camp. I also watched PSG suffer a similar fate, at the same stage of the competition, at the hands of Real Madrid the following year.

The seven-time French champions had been considered strong contenders every season, particularly after the Qatar Sports Investments takeover began in 2011.

Yet for all the big names, glamour and domestic glory, they only got as far as the last 16 of the Champions League in the last two seasons. They were sitting at Europe's top table, but without the silverware to show for it.

For me, it feels as though the burden of expectation has weighed heavily over the past two years and a mental fragility has emerged. They have hardly had the luck of the draw either.

What struck me around that Nou Camp match was the 'European giant' mentality of Barcelona. There was no imposter syndrome here.

It was clear from then-manager Luis Enrique and forward Luis Suarez at the pre-match news conference that Barca meant business. They believed the tie could be turned. I think we all believed it was possible, just not very probable.

Unfortunately, the problem for PSG was that they believed it too. Football is as much psychological as it is tactical or physical and this was a stark reminder.

Paris St-Germain were beaten 6-1 in the second leg of their 2016-17 last 16 tie against Barcelona

Suarez scored after just three minutes. Once Barca were on the front foot, they seized control, smelled blood and PSG duly crumbled. Even when Edinson Cavani got the all-important away goal to make it 3-1, Barca didn't let up.

On a Champions League matchday, I will normally head down to the post-match 'flash' area for one-on-one interviews around 10 minutes before full-time.

However, my producer and I were rooted to the spot. There was something in the air. Everyone in the stadium could feel it. Three goals in seven minutes followed and the Nou Camp went bonkers.

After the game, Neymar told me it was the best match of his career. Ivan Rakitic compared it to the New England Patriots' historic comeback Super Bowl win just a week earlier.

Both admitted their absolute belief was what carried them through. I posted a video of the mad scenes in the press box external-link after Sergi Roberto's historic goal, which went viral on social media. It was a moment in time. We couldn't believe what we had seen. What a privilege to be there.

Paris St-Germain in the Champions League Season Stage reached 2012-13 Quarter-finals (3-3 agg v Barcelona - away goals rule) 2013-14 Quarter-finals (3-3 agg v Chelsea - away goals rule) 2014-15 Quarter-finals (1-5 agg v Barcelona) 2015-16 Quarter-finals (2-3 agg v Man City) 2016-17 Last 16 (5-6 agg v Barcelona) 2017-18 Last 16 (2-5 agg v Real Madrid)

Wounded but ready to fight again, PSG acted swiftly. Prescribing to the old adage of keeping your enemies close, they signed the architect of that painful defeat, Neymar, for an eye-watering £200m world-record fee that summer.

Kylian Mbappe followed on loan, after a breakthrough year which included the Ligue 1 title and reaching the Champions League semi-finals with Monaco.

Yet it was deja vu the following season, this time against champions Real Madrid. The 'please don't let this happen again' look on the players' faces transpired through their nervy actions on the pitch.

Neymar could only look on as the Bernabeu celebrated Cristiano Ronaldo's 100th Champions League goal. PSG were dealt a huge psychological blow with the Brazilian injured for the second leg, but by the time Real Madrid completed the job in Paris, 5-2 on aggregate, even the French press had turned on them.

Paris St-Germain were beaten 5-1 over two legs by Real Madrid in last season's last 16

Barcelona and Real Madrid had the aura, experience and belief to kill off PSG. Far from galvanising them into causing an upset, the Parisians imploded under the pressure two years in a row.

As they face another verified European heavyweight in Manchester United - without their injured talisman Neymar - you wonder if history will repeat itself again.

The idea of facing an unconvincing United under Jose Mourinho went down well in Paris. The thought of overhauling a rejuvenated United under Ole Gunnar Solskjaer is an altogether different prospect.

There are no easy games at this phase of the competition, but these two legs against United could prove a huge test of PSG's mental resolve under new boss Thomas Tuchel.

The owners are on a mission for European glory, but it must be remembered that success on this stage doesn't come overnight either.

Chelsea won the trophy in 2012, nine years after Roman Abramovich poured his millions into the club. Manchester City are another example of a big club with new money who are facing similar hurdles. With that in mind, PSG are largely on track, in terms of time.

With World Cup experience under the belt for many, it will be fascinating to see whether this group of players have mastered the 'sangfroid' needed to survive the heat of a European battle, or if it will be another case of stage fright at their latest audition.