The teams played for 120 minutes, with one OKC group getting a full 90 and another playing the additional 30.
El Paso took an early lead after a bouncing ball in the box from a corner kick found a Locomotive striker for the close-range conversion.
The Greens had a couple of great opportunities to level the score in the first half with Omar Gordon hitting the post with an overhead kick and Rafael Garcia narrowly missing a penalty wide of the left post.
Locomotive FC doubled the lead in the second half via an own goal from an Energy trialist. A dangerous cross from the left wing was inadvertently knocked past goalkeeper Cody Laurendi from inside the six-yard box.
Defender Kyle Hyland was medically cleared to play after offseason surgery and made his first competitive appearance of the preseason, playing the entire second 45 minutes.
In the final half hour of play, the Greens were on the front foot, pressing El Paso and creating several chances. Defender Zach Ellis-Hayden came closest to cutting the lead in half with a left-footed effort from the top of the penalty area that just sailed over the bar.
El Paso added a third against the run of play with a long-range effort that found the top corner.
The Greens wrap up preseason play in Tucson, Saturday, February 29 at 11 a.m. against FC Tucson.
Energy FC begins the 2020 USL Championship season at Taft Stadium March 7 at 7 p.m. against Colorado Springs Switchbacks FC. Season seats for the 2020 season are on sale now. Visit https://www.energyfc.com/tickets or call 235-KICK for more information.