Frenchman Lenglet's first league start since his 36 million-euro move from Sevilla turned sour when he was shown a straight red card in the 35th minute at the Nou Camp following a coming together with Pons, after referee Jesus Gil Manzano consulted the video assistant referee (VAR).
Barca lead the standings on 39 points from 18 games, three clear of second-placed Real Madrid who host Athletic Bilbao on Sunday.
A second half double from Karim Benzema helped Real Madrid to a 4-1 victory at Girona on Sunday and maintain their perfect La Liga start in the post-Cristiano Ronaldo era.
Barcelona's 100 per cent start to the season was ended by Catalonian neighbours Girona, who picked up a draw at the Nou Camp, allowing Real Madrid to take advantage with a victory over Espanyol.
PSG made hard work of beating Strasbourg 4-2 in the French Ligue 1, while Real Madrid registered a comfortable 4-1 win away to Alaves in their opening game.
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