Isn't it up to Pep to rein back his forward runs?
Mendy played in a very advanced role, doing very little defending, at Bournemouth. Pep will surely have discussed his first game with him in some detail. If Pep was concerned about his positioning and failure to track back he would have told him. But on Saturday he played just as far forward. If Mendy wasn't playing to his manager's instructions, wouldnt he have been taken off at half time on Saturday? He had provided very little support for Otamendi and hadn't featured much in attack. Instead, in the second half he pushed forward even more, to greater effect. Pep is continually speaking to defenders during the game about their positioning, particularly those close to him. I didnt see any signs of him encouraging Mendy to drop deeper to support Otamendi,
The only logocal conclusion that can be drawn from Mendy's first two games is that Pep is happy for him to focus primarily on attacking.