Martinez netted a brace as defending champions Atlanta crushed the 10-man Houston Dynamo 5-0 at Mercedes-Benz Stadium.
After Alberth Elis was sent off in just the sixth minute for making contact with the referee, Darlington Nagbe got the scoring started for the hosts before Brandon Vazquez's close-range header made it 2-0.
Martinez's header from a Julian Gressel cross extended Atlanta's lead on the hour-mark before the Venezuelan finished brilliantly again 19 minutes later.
Atlanta United FC (@ATLUTD) July 18, 2019
The striker has scored six goals in four games since returning from the Copa America, while Gressel sealed Atlanta's win.
Frank de Boer's men moved into second in the Eastern Conference, sitting three points behind leaders Philadelphia Union.
At BMO Field, Altidore's fine goal led Toronto to a 3-1 win over New York Red Bulls.
Altidore produced a brilliant flick from a Tsubasa Endoh cross to give the hosts the lead before Alejandro Pozuelo's penalty.
Toronto FC (@TorontoFC) July 18, 2019
Tom Barlow pulled a goal back for the Red Bulls in the 63rd minute, but Ashtone Morgan's strike helped lift Toronto into sixth in the east.