Jonathan David scored the only goal as Lille defeated PSG to go three points clear at the top of Ligue 1 in a match that saw Neymar sent off in the closing stages on his first top-flight start since January 31.
PSG have now lost three straight home Ligue 1 games for the first time since October 2007, although Neymar missed two great chances and the hosts will feel they did enough to take at least a point.
Under Pochettino, PSG have mixed some barnstorming performances – such as the 4-1 win at Barcelona in the Champions League last 16 – with some underwhelming ones.
For the Argentine, though, the uncertainty facing all teams this season due to the coronavirus pandemic is not a valid reason for PSG's patchy form.
"It could happen in some games; these are the circumstances [contrast of beating Barca and losing in Ligue 1]," he said.
"You might tell me; these are excuses if we talked about these weird circumstances around football. But this is the reality.
"We are team with lots of ups and downs since the beginning of the season, we are not consistent for different reasons.
"Some situations are real. We are working on it. We are missing that consistency.
"It is very difficult to justify a defeat, because today we have not been to the level that is assumed with this team, the PSG.
"This a consequence of real facts that make us to have these ups and downs. But I think we can solve it over the time."
PSG are now three points adrift of Lille with only seven games remaining but Pochettino said he felt the fight for the title would go to the wire ever since he arrived as Thomas Tuchel's replacement in January.
"The truth is I am disappointed for the result, for the performance and the important three points missed as we already talked about it before the game," added the former Tottenham boss.
"I am not worried, since we arrived three months ago, it is a situation where we are going to have to fight until the end to see who will win the competition."