The pair of former Premier League regulars were already feeling the heat as fans began to turn on them, and things got even worse against Al Hilal.
In a big Saudi Pro League clash between the two PIF-owned teams Al Hilal came out on top with a 3-1 win.
Former Fulham great Aleksandar Mitrovic got on the scoresheet despite earlier missing a penalty, making it 12 goals in 13 games for his new side.
However, things could have hardly been more different for his opposite striker, Liverpool legend Firmino.
The 32-year-old is now on a ten-game scoreless streak since a hat-trick on his debut, and is facing calls to be dropped for the national team's no.9 Feras Al-Buraikan.
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Things were arguably worse for his countryman Roger Ibanez, though.
Allan Saint Maximin had cut the scoreline to 2-1 just before the hour mark, and Al Ahli were searching for an equaliser.
The former Roma centre back had a simple header back to Mendy to collect and restart an attack, but instead he nodded it straight past and into the back of the net past the ex-Chelsea shot stopper.
Ibanez collapsed to the floor in embarrassment, and Mendy wasn't at all happy, praying to the skies in disbelief.
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Al Ahli had been on a decent run before the match, but that was largely without much help from Firmino, who's only going to have more pressure on his shoulders for a torrid start.