>>3066717 (lb)

https://en.wikipedia.org/wiki/List_of_Justices_of_the_Supreme_Court_of_the_United_States_by_seat

According to this they are numbered and not in the order you are listing.

Chief Roberts I would assume would be #1 as the next numbered seat is the vacant seat and awaiting Kavanaugh. The next seat numbered in order is Breyer, making him #2.

#1 = Roberts

#2 = Breyer