Mahut has won both their previous matches. Both were on indoor courts in the last 12 months. Their sets were close.
Mahut doesn’t have a good record on clay though he reached the third round at the French Open last year.
Pouille has been playing well recently on hard courts. He has a decent record on clay. He reached the semis in Hamburg last July.
I see a little value on Mahut at the start but the slow courts won’t be to his liking. He only won 1 first round match in Monte Carlo which was in 2014 when he beat Thiem.
Three sets seem likely.