Cam Weaver scored in the 49th minute and had two assists as the unbeaten Houston Dynamo moved to the top of Group 3 with seven points, three ahead of Olimpia in CONCACAF Champions League play.
The 29-year-old created the opener for former Derby County and West Brom midfielder Giles Barnes, who unleashed a left-foot shot past FAS keeper Daniel Arroyo in the 21st minute.
Dynamo doubled their lead just before the half-time break when defender Bobby Boswell rose at the far post and headed home, much to the delight of the crowd at BBVA Compass Stadium.
Four minutes into the second half it was Weaver's turn to find the back of the net, taking full advantage of the El Salvador club's defensive struggles.
After Adam Moffat hit the bar with a 20-yard volley, second half substitute Calen Carr scored the fourth goal, once again made by Weaver.
The tall striker took a pass from Kofi Sarkodie before finding Carr who scored with a right-footed chip.
And Guatemalan side Municipal moved level with Group 6 leaders Monterrey on six points thanks to their 2-1 win over Panamanian outfit Chorrillo.
The visitors took the lead in the first minute through Renan Addles, but goals from Mario Rodriguez and Leandro Barrios helped Municipal come from behind and take the win.