In Petrie's sophomore season at Princeton, the team was co-champion of the Ivy League with a 20-6 (12-3 Ivy) record. Despite the fact that Princeton had three of the five first-team All-Ivy team members, including Petrie plus second-team member John Hummer, they lost the one-game league playoff to the Jim McMillian-led 1968 Columbia Lions men's basketball team. That year the team rose to as high as 8th in the AP Poll. The following season, Petrie led the Ivy League in scoring (23.9 points/game in conference games), and the team accumulated a 19-7 (14-0) record, including an appearance in the 1969 NCAA Men's Division I Basketball Tournament. They lost to St. John's in the tournament, but Petrie was again on the first-team All-Ivy squad. As a senior, Petrie was second-team All-Ivy, but the Tigers placed third in the conference to the undefeated (in Ivy League games) Corky Calhoun-led Penn Quakers men's basketball team and McMillian's Lions. Although Princeton did not appear in the 1970 NCAA Men's Division I Basketball Tournament, they hosted Penn's game. All three of his varsity years were spent under head coach Pete Carril. Petrie was co-captain of the 1969–70 team with classmate Hummer. Petrie was All-East both as a junior and a senior.