Quincy Mayor Thomas P. Koch will square off in November against his predecessor, William J. Phelan, after the two candidates topped a four-way mayoral field in the city’s recent preliminary election. Koch far outpaced his preliminary rivals, collecting 6,670 votes to 3,514 for Phelan, 3,066 for City Councilor Doug Gutro, and 3,037 for School Committee member Anne Mahoney. Koch, who is finishing his fourth term, unseated Phelan in 2007 and then turned back a challenge from him in 2009. In other preliminary election results, incumbent Brad L. Croall cruised to a strong first-place showing in the race for Ward 2 councilor, picking up 1,466 votes to 425 for James M. Connors and 110 for Gulistan M. Malik, both first-time candidates. Croall and Connors will vie in the Nov. 3 general election. Ian Cain and Karl Roos will compete in November for the seat of retiring Ward 3 Councilor Kevin F. Coughlin after outpacing Sandy Verhault in the preliminary. Cain picked up 1,099 votes, Roos, 858, and Verhault, 696. Cain is making his first bid for office, while Roos ran previously for School Committee and state representative.