Halak, who was acquired from Montreal in the offseason, hadn't played since losing 3-1 to Colorado in the Blues' exhibition opener Sept. 21. Ben Smith scored for the defending Stanley Cup champions but Halak stopped a penalty shot by Jeremy Morin with 4:05 left to help preserve the win.
David Perron and Alex Steen both scored their fourth preseason goal for St. Louis (4-2-0). T.J. Oshie and Matt D'Agostini also scored.
Marty Turco, who allowed all three goals, made 23 saves for the Blackhawks. Chicago (1-4-0) left top-line players such as Duncan Keith, Marian Hossa, Patrick Sharp and Jonathan Toews at home.