Winchester guided Andy McDonald's centering pass through Turco's pads at 9:01 of the opening period. Armstrong made it 2-0 at 14:11 with his third goal of the preseason, converting on another man-advantage situation.
Johnson's rebound at 6:02 of the second period extended the Blues' lead to 3-0, and Steen made it 4-0 3:02 later.
Each team has one preseason game left before opening the regular season next weekend. The Stars get underway at home against Nashville on Oct. 3 and the Blues meet Detroit on Oct. 2 and 3 in Stockholm, Sweden.
Copyright by STATS LLC and The Associated Press
Arena: American Airlines Center Location: Dallas, Texas
Attendance: 16,260 (87.7% full)
Brad Winchester (power play) Assist: Andy McDonald, Derek Armstrong
Derek Armstrong (power play) Assist: David Backes, Erik Johnson
Erik Johnson Assist: Patrik Berglund, Brad Winchester
Alex Steen Assist: Jay McClement, Barret Jackman
David Backes (power play) Assist: Derek Armstrong, David Perron