Money can't buy you love and nor, funnily enough, can peevish displays of entitlement. Paris Saint-Germain are discovering this, as what was supposed to be a night of celebration ended in disappointment and disgrace. Victory at home to Valenciennes on Sunday would have all but guaranteed the club their first title in 19 years and kept them on course to equal Lyon's record points tally from 2007, but they stumbled to a 1-1 draw after which, rather than earn praise for wonderful play, PSG were condemned for arrogant behaviour. Again.

Of course, that is not how PSG see it. They believe they are being persecuted and it is true that the referee, whom they feel ruined their chances of opening up a nine-point lead over Marseille with three matches to go, was extremely pernickety, punishing virtually every foul with a card – and sending off Thiago Silva for gently laying his hands on him while the PSG captain was complaining about a free-kick being awarded to Valenciennes. The letter of the law says players cannot touch the officials so Alexandre Castro felt justified in showing the Brazilian a straight red but as there was clearly no aggression in Silva's contact it seemed an extraordinarily pedantic decision – but that does not excuse the reaction of PSG, least of all their director of football, Leonardo, who argued with the official throughout half-time and then, at the end of the match, shoulder-barged him in the tunnel before being pulled away by his president, Nasser al-Khelaifi.

"Of course I am angry, what happened is beyond all logic and it pisses me off," said Leonardo later, apparently still not having calmed down. "We already had four players suspended today and then we get another red. Keep this up and we'll no longer have a team to play with. It's unacceptable and impossible." Khelaifi usually seems embarrassed by the spoilt oaf who occasionally emerges from Leonardo's slick exterior, especially in March when the Brazilian disdainfully explained away a defeat at Reims by intimating that his team were too good for Ligue 1 and better suited to the Champions League, but on Sunday night the Qatari seemed to share his employee's bitterness and suggested that people's failure to just accept PSG's superiority risks making the league look silly. "We wanted to be champions tonight but a lot of things happened out there," said Khelaifi. "I don't want to say more but people saw. It doesn't change much for PSG but for the atmosphere in Ligue 1 it changes a lot."

PSG have been feeling aggrieved pretty much all season, ever since the second match of the campaign, against Ajaccio, when Ezequiel Lavezzi was harshly dismissed for a tackle that seemed fair and then Carlos Ancelotti was shown a red card when the manager kicked over a bottle of water in frustration. "A lot of people are against us," said the midfielder Blaise Matuidi as he came off the pitch on Sunday night, though he himself hardly sought to increase the club's popularity when he provocatively celebrated last week's win over Evian right in front of the opposing dug-out, ensuring that a spite-filled match ended in a mass brawl. PSG were shown two red cards during that game – one for a dangerous tackle by David Beckham and one to Marci Verratti for persistent whinging – and the goalkeeper Salvatore Sirigu was sent off after the final whistle for an altercation in the tunnel, although the referee did not actually show him the red card because the goalkeeper refused to come out of the dressing room when summoned, conduct that could have been punished with a ban of up to eight games. A disciplinary panel eventually decided to ban Sirigu for just two matches but PSG fans complain that such leniency is rare in a season during which the club has seen more red cards – nine – than anyone else. Others have less sympathy, saying the Parisians' indiscipline stems from their haughty belief that everything should go their way and their inability to control themselves when it doesn't. Even in the Champions League PSG have provided evidence to support that theory, notably when Zlatan Ibrahimovic was dismissed in the first leg of the last 16 tie against Valencia for splenetically booting Andrés Guardado after being dispossessed as he tried to waste time.

All of the above explanations have merit but it has also become clear that another cause for PSG's irritability in recent weeks has been plan old jitters. Since being beaten to the title by Montpellier last season, and then investing heavily again in a bid to quash all uppity rivals, PSG have been playing under a colossal weight of expectation. They have so much more quality than everyone else in the league that they have usually found a way to win and after Christmas they began to do so with style, but recently an edginess has returned to their play. They only squeezed past little Evian last week, and against relegation-threatened Valenciennes, on a day in which it was confirmed that the club has already booked a ceremony at the Place de la Trocadéro and a procession down the Seine to celebrate winning the title, the high stakes seemed to paralyse the team.

PSG moved slowly and unsurely and as early as the seventh minute an agitated Ancelotti, who spent much of last week warning against the twin ills of complacency and intense pressure, was urging his enfeebled team to play farther forward and at a higher tempo. His players could not shake off their tension and their touch remained heavy, their passing wonky. "We felt their nerves," said the Valenciennes manager, Daniel Sanchez, whose team took the lead through a fine counterattack in the 17th minute, Gaël Danic converting the rebound from a powerful 20-yard drive by Vincent Aboubakar. "After that they became impatient and angry," said Sanchez. Silva's dismissal before half-time deepened PSG's fury but not until the final 15 minutes did they start to respond in a positive way, as Javier Pastore and Christophe Jallet began at last to get behind the opposing defence down the right and Ibrahimovic was given more to work with than hopeful punts. Alex equalised with a header from a corner in the 82nd minute and Valenciennes had to defend valiantly in the last few minutes to prevent PSG from getting a winner that, given their hugely positive goal difference, would have effectively given them the title. Perhaps, though, it would be more fitting if they sealed it next weekend – away to Lyon, whose record of six straight titles from 2002 and 2008 is already being targeted by some PSG fans. What was that about Parisian complacency?

• This article was updated on Monday 7 May 2013 to reflect the fact that Zlatan Ibrahimovic was sent off in a last-16 tie against Valencia, not a quarter-final against Málaga