The Venezuelan forward headed in a Julian Gressel cross for the opening goal – and MLS record – in the 42nd minute against New York City at Mercedes-Benz Stadium.
Martinez continuing his hot streak meant he surpassed the previous best mark he briefly shared with Portland Timbers star Diego Valeri.
The 26-year-old has netted 14 times during his run, which started in May, to close in on Los Angeles FC star Carlos Vela atop the MLS goalscoring charts.
Vela has struck 22 times for the Western Conference leaders, while Martinez is up to 20 goals after adding another with a penalty later in Sunday's match.
Former Torino forward Martinez enjoyed a stellar season in 2018, too, scoring 35 MLS goals to be linked with a return to Europe.