If I'm invited to a baby's christening, and then the party after at a restaurant, is it rude to just attend the party?

i know when people are invited to wedding receptions, they may or may not attend the wedding, depending on time and a bunch of factors. i am invited to a friend’s son’s christening this weekend, and the party afterward at a restaurant. i am considering (actually planning) to attend just the party. i am wondering if this would be considered rude or not a big deal.