Squandering an opportunity to take over the top spot in the OUA West, McMaster conceeded an early brace to Windsor's Leighton Speechley-Price en route to a 2-1 loss on the road Sunday.
The scrappy encounter saw Windsor issued a red card when Tony Falkestajn was given a second yellow, and two Marauders issued cards at the conclusion of the match.
Stefan Scholz provided the silver lining for Mac on Sunday, scoring his second goal in as many days to make a match of it in the 58th minute.
With the loss, the Marauders fall to 8-3-0 on the season, while the Lancers improve to 9-1-1 atop the divsion.
After suffering their first loss in six matches, McMaster will look to reenter the win column on Saturday, October 10, when the Marauders play host to the Algoma Thunderbirds at Ron Joyce Stadium.