It was 2-all in the eighth before Seattle scored three times off reliever Jonathan Hernandez (5-1) before making an out.
Marmolejos atoned for twice making the last out of an inning with the bases loaded. Evan White followed with another run-scoring single and Phillip Ervin added an RBI double in his first game for the Mariners.
Seattle has now won four in a row and 10 of the last 14, largely with a group of young players in a rebuilding year.
''The goal here was just to get better along the way and you're seeing that,'' Seattle manager Scott Servais said. ''You're seeing it play out and it's been fun to be a part of it.''
The Rangers have lost four in a row and six of seven.
Shin-Soo Choo had a season-high four hits for Texas, including a ninth-inning homer.
''He's a pretty integral part of what we're trying to do right now, because his at-bat quality on a daily basis is really important for our young guys to see,'' Rangers manager Chris Woodward said. ''He's a really valuable piece right now for us.''
Seattle starter Justus Sheffield allowed two runs over seven innings. He had one of his best games of the season and looked to be in position for the win until he made his only real mistake of the night just before the very end of his outing, giving up a two-out, tying homer to Anderson Tejeda in the seventh.
''Sheff was dynamite tonight,'' Servais said. ''I know he wants to get that one pitch back on the home run he gave up there in the seventh. But really happy with how he continues to throw the ball and progress.''
Sheffield has now lasted at least six innings while allowing two runs or fewer in four of his last five starts.
Joey Gerber (1-0) pitched a scoreless eighth and Yohan Ramirez worked the ninth for his second save.
In the seventh, Rangers relief pitcher Joely Rodriguez fell to the ground after throwing a pitch to Kyle Lewis. He stayed on the ground for some time holding his left leg and needed assistance as he limped off the field. ''It's a left hamstring strain,'' Woodward said. ''It didn't look good. Just based on talking to him as he's walking off the field. He could barely walk, he could barely get up. I don't expect him to honestly be back.'' ... Before the game, Texas manager Chris Woodward said pitchers Corey Kluber and Jose Leclerc, both on the injured list since July with right shoulder muscle tears, will not return this season. Danny Santana, on the 10-day IL since Aug. 27 with a right elbow strain, is also likely out for the season. ... OF Willie Calhoun (left hamstring sprain) and 2B Rougned Odor (eye infection) could return at some point during the Rangers upcoming homestand. Woodward said Odor will not play every day when he returns to give younger players more opportunities.
Prior to the game, the Mariners claimed right-handed pitcher Casey Sadler off waivers from the Chicago Cubs, optioned outfielder Jake Fraley to the alternate training site and added Ervin to the active roster. Ervin, who was claimed off waivers from Cincinnati on Thursday, started in right field on Saturday. He hit .086 with the Reds this year. ''It's a fresh start, a new opportunity to showcase my skills to other people,'' Ervin said. ''Got off to a good start, got a hit. I'm looking forward to it.''
Rangers: RHP Jordan Lyles (1-3, 8.59 ERA) has allowed at least three runs in his last six appearances.
Mariners: RHP Justin Dunn (2-1, 4.33) has thrown 12 scoreless innings in his last two starts. Dunn has faced the Rangers twice this season, winning both starts while allowing two runs in 12 total innings.
More AP MLB: https://apnews.com/MLB and https://twitter.com/AP-Sports
Copyright 2020 STATS LLC and Associated Press. Any commercial use or distribution without the express written consent of STATS LLC and Associated Press is strictly prohibited.