I don't see Brentford causing Chelsea too much trouble, even though they've been a revelational team so far this season, I'm going to be of the opinion that the momentum would drop along the season. it might not be an easy win for the blues, especially just coming back from the International the teams with lesser players representing their national team are always having a slight advantage imo.
There is not just fatigue from internationals in play here, couple of Chelsea players also returned with small injuries. It is not certain that Lukaku and Rudiger will be able to play this game. They are important parts of Chelsea team and while they will manage to sub Rudiger I feel like Chelsea can't replace Lukaku and what he is doing for the team. Will be waiting for news before picking my scores.