HONG KONG — The prequel to cop thriller “Infernal Affairs” broke box office records with an opening-day gross of $506,212 on the Oct. 1 holiday.It raked in $168,222 on Tuesday, when there was an evening of sneak previews, bringing in a total of $672,892 in two days. First day’s take for “Infernal Affairs II” beat the original’s opening and becomes the highest box office opener in October in Hong Kong’s history. It also is the best opening pic this year. Prequel, helmed by Andy Lau, examines the roots of the conflict between the original film’s crime boss and police chief. Pic stars Anthony Wong, Eric Tsang, Francis Ng, Hu Jun, Edison Chen, Shawn Yue and Carina Lau.