The Frenchman was very disappointed with his team's heavy loss, but stressed that they have no reason to be concerned as they have still had a good start to the season
OM fell 1-0 behind early on when Bafetimbi Gomis converted a penalty, and they were unable to get themselves back into the game as the guests cruised to a comfortable victory.
"It has been a really tough night in terms of the result and Rod Fanni's red card. In fact it has been a horrible night," Baup told the official Ligue 1 website.
"We conceded really fast, and then failed to equalise even though we had a few chances. Then we conceded a second and then the third, which killed off the match.
"It's very hard to take, a really awful night. Our opponents were superior, and there is a whole raft of things we need to correct.
"But we mustn't focus on this result - we've played 13 other good matches - and now we need to go and pick up some points in Brest."
Marseille currently sit third in the Ligue 1 table with 26 points from 14 games.