(Adds later games)
By Julien Pretot
PARIS, Jan 22 (Reuters) - Paris St Germain were knocked out of the French Cup and Monaco striker Radamel Falcao suffered what could be a serious knee injury on a bad night for the top sides on Wednesday.
Champions and Ligue 1 leaders PSG slumped to a 2-1 home defeat by Montpellier, for whom Victor Hugo Montano scored the winner with a powerful 69th-minute header after Edinson Cavani had cancelled out Daniel Congre's opener in the first half of the last-32 match.
PSG, who suffered their third defeat in all competition this season and their first home loss since November 2012, were denied a late penalty when referee Olivier Thual waved play on after Cavani had been brought down by Jamel Saihi.
PSG coach Laurent Blanc, who started with top striker Zlatan Ibrahimovic on the bench, sent on the Swede in the 66th minute but there was nothing the former Barcelona and AC Milan forward could do to change the result.
"It's a big achievement, it's extraordinary, it helps us forget a little bit about our bad start to the season," Montpellier president Louis Nicollin told Eurosport.
Montpellier, the 2012 French champions, are 16th in Ligue 1. Monaco, who are second in the standings, reached the last 16 with a 3-0 win at amateurs Chasselay Monts d'Or Azergues but they were left to sweat on Falcao's fitness.
The Colombia striker opened the scoring in the 29th minute but was carried off the pitch on a stretcher shortly before the break after being tackled by Chasselay defender Soner Ertek.
"We lose Radamel Falcao. It's a big blow. I think it is serious. The news is not reassuring," captain Jeremy Toulalan told Eurosport.
Monaco said in a statement that Falcao had sustained a knock to his left knee and they were awaiting further checks to assess the injury.
Striker Emmanuel Riviere netted the two other goals in a one-sided encounter at Lyon's Gerland stadium as fourth division team Chasselay, with former Monaco and France winger Ludovic Giuly in their ranks, failed to pose a threat.
Ligue 1 teams Girondins Bordeaux and Toulouse fell victim of "La Magie de la Coupe" (the Cup's magic) when they were knocked out by amateurs Ile Rousse and Moulins respectively.
Ile Rousse, a Corsican side who play in the fifth division, won on penalties after a goalless draw and fourth division Moulins prevailed thanks to a Sebastien Da Silva double. (Reporting by Julien Pretot, editing by Ed Osmond)