ARLINGTON -- The Mariners' 6-3 loss to the Rangers on Friday night at Globe Life Park marked the end of one starting pitcher's string of effective outings, but it also highlighted the continuation of a solid run by a bullpen that has experienced its share of turnover this season.

Lefty Marco Gonzales allowed six runs (five earned) over 5 2/3 innings, breaking a streak of four starts in which he allowed three runs or fewer. Gonzales ended August with a 4.63 ERA, falling short of adding to his career-high win total, which reached 14 after his past outing against the Blue Jays on Sunday, when he allowed one run over seven innings.

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Friday’s outing wasn't as efficient, though Gonzales was in control for most of his 100-pitch performance. He also wasn't helped by his defense, which forced the lefty to throw more pitches and face more hitters, which could have contributed to his ineffective sixth and final frame.

"You do need to make the plays," Mariners manager Scott Servais said. "We didn't get it done tonight. It does happen once in a while. We hadn't done that in a while."

Shortstop J.P. Crawford committed the first error in the third inning when he was not able to get a handle on an Elvis Andrus ground ball. Two innings later, Kyle Seager attempted a backhand snag of an Andrus sharply hit ground ball, but the ball clanked off his glove. Seager then made another attempt to snag it with his glove, but the ball popped out.

Instead of a potential inning-ending double play, the Rangers scored to take a 3-2 lead, and Gonzales had to face two more batters.

"I got an in-between hop and didn't come up with it," Seager said. "That [double-play attempt] would have been the only play. When I got the in-between hop and it took me backwards, I wouldn't have had a play at home."

In Gonzales' final frame, the Rangers were able to chip away. They plated three runs behind a leadoff homer by Danny Santana and a two-run double by Jose Trevino, who logged three hits on the night.

"I just wasn't as crisp as I'd like to be," he said. "A little bit up in the zone. Just kind of need to put more focus on executing pitches and really just bearing down and getting myself out of that inning."

It marked just the third time in Gonzales' past 15 starts in which he gave up more than four runs.

"I thought Marco was sharp early on," Servais said. "Getting in a little bit of trouble there, he was trying to work his way through it. The ball kind of got up on Seags. It's a play Kyle usually makes. You get the big out there, turn the double play and move on down the road. It just didn't happen tonight. I thought Marco's stuff was fine. He competes like he always did. Just not our night."

Following Gonzales's departure, Servais needed to turn the game over to only one reliever, Erik Swanson, who shut down the Rangers' offense. Swanson struck out five of seven batters he faced, extending a dominant stretch for the bullpen, which has compiled a 2.20 ERA since Aug. 13.

"Our bullpen is really attacking hitters," Swanson said. "We're not walking people right now. We're just going after guys, having success with that. That's what we preached from the beginning of the season. We're doing that right now."

Seattle relievers have allowed 11 earned runs across 45 innings, with 17 walks and 52 strikeouts in 11 games not started by an opener during that stretch.

"The last month or so, the guys are starting to settle in," Servais said. "We're throwing the ball really good. We're not walking people. We're throwing strikes and guys down in that bullpen have stuff to strike people out. It's been a nice boost for us. Tonight, Swanny was great, and he'll continue to build off that."

Swanson, who began the season as a starter, has not allowed a run in his past six relief appearances. He has 11 strikeouts in that span.

"It's taken a little bit to get a routine down in the bullpen after starting for so long," he said. "But relieving has been something I've done in the past. As of late, I feel like my routine is getting a lot better and things are starting to click for me."