South African World Cup winner Handre Pollard kicked 13 points but his Montpellier side suffered a last-gasp 26-23 defeat in the opening game of the new French Top 14 season on Friday.
In a match where they conceded 22 penalties and saw two yellow cards, Montpellier finally paid for their indiscipline when a penalty try settled matters for the visitors.
It had been 187 days since the last Top 14 game was played with the sport put on hold due to the coronavirus.
The disease still casts a huge shadow over the championship.
Montpellier announced on Wednesday that an unnamed player and a member of their coaching staff had tested positive for Covid-19.
Meanwhile, Stade Francais recorded a reported 25 positive cases of the virus last month and were forced to call off their planned Friday opener against Bordeaux.
On Friday, a power cut early in the first half at Montpellier's GGL Stadium was an extra headache.
However, unlike many sports in other nations, at least the club had the honour of being able to welcome fans back with a maximum of 5,000 spectators allowed.
Montpellier scored all of their points in the first half with Yacouba Camara and Caleb Timu scoring tries and with Pollard accurate with the boot for a 23-10 edge.
Scrum-half Clovis Le Bail kept Pau in touch with a 23rd minute score.
But back came Pau with a last-minute penalty try to claim victory although Montpellier had a 47th minute try by Gabriel Ngandebe ruled out for an infringment by Camara who was sin-binned for his troubles.