While D.C. United has lost its first three Group A games and looks headed toward a first-round exit, and two-time defending MLS Houston has tied its first two games in Group B, the USL clubs are well poised to reach the knockout round.
Wednesday's match was the fourth game of five games in 10 days for the Montreal, which is at the semifinal stage of the USL-1 playoffs. Brown scored in the third minute by heading home Joey Gjertsen's corner kick. Brown scored the winning goal from the penalty spot in the 70th minute, before two Olimpia players were ejected.
Elvis Turcios' goal for Olimpia in the 34th minute from a 28-yard free kick was the first conceded by the Impact and goalkeeper Matt Jordan in five Concacaf Champions League game.
In Guatemala, Municipal escaped with a 2-2 tie against the visiting Islanders' thanks to Juan Carlos Plata's 89th minute goal. Puerto Rico, resting several regulars in light of its upcoming USL-1 playoff games, had opened the scoring in the 10th minute when Fabrice Noel juked past three Municipal defenders and stroked a shot keeper Paulo Cesar Motta.
Carlos Cesar Leguizmon equalized for Municipal in the 79th minute. With two minutes left, Sandy Gbandi put Puerto Rico ahead after settling a cross from Scott Jones and slipping his shot into the net for a short-lived lead.
Both the Impact and the Islanders' unbeaten streaks include three group games and two preliminary round games.
On Friday, Montreal hosts Vancouver and Puerto Rico travels to Rochester in USL-1 first-leg semifinal games.
Olimpia (Turcios 34) 1 Montreal Impact (Brown 3, 70) 2
STANDINGS: Montreal (7 points), Atlante (4), Olimpia (3), Joe Public FC (0)
Atlante & Joe Public meet on Thursday.
Municipal (Leguizmon 79, Plata, 89) 2 Puerto Rico Islanders (Noel 10, Gbandi 88) 2
STANDINGS: Puerto Rico (7 points), Tauro (3), Santos Laguna (3), Municipal (1).
Tauro & Santos Laguna meet on Thursday.