SEATTLE -- The only question was whether the ball would stay fair. When Seattle third baseman Kyle Seager roped a fly-ball down the left-field line with a runner on first base in Sunday's eighth inning, the Mariners were a fair ball away from tying the score.

Or so they thought.

Seager's ball did stay fair, but Colorado left fielder Brandon Barnes made sure it didn't drop as he saved the Rockies' lead with a diving catch in the corner. Barnes, having slammed his chin and rib cage into the dirt, then got up and made a perfect throw that was relayed into an inning-ending double play as Colorado held on for a 3-2 win over the Mariners.

"I would say that's probably one of the top 10 plays of the year," Seattle manager Lloyd McClendon said after the loss. "From where he came to where he got to, and then to make the throw to first."

The Rockies, having taken advantage of a Seattle throwing error four innings earlier, turned the incredible defensive play into a win and their first series victory of September.

"With a one-run lead, I'm just trying to do anything I can to help the team win," Barnes said.

The Rockies jumped out to a 3-0 lead on Seager's throwing error in the top of the fourth inning. Colorado designated hitter Willin Rosario and first baseman Justin Morneau both scored on Seager's errant throw to home with the bases loaded, giving the Rockies a 3-0 lead.

"That's a tough play, a body-control play," McClendon said. "It would have been a heck of a play if (Seager) got him."

Seattle (69-75) came back to score twice in the bottom of the fourth but got shut down by starter Kyle Kendrick and four Colorado relievers the rest of the way.

The Rockies' bullpen allowed just two hits over four shutout innings, with closer John Axford earning his 23rd save. Kendrick (6-12) allowed two runs off three hits over five innings.

"He's been throwing the ball well since he's come back," manager Walt Weiss said after Kendrick's third start since coming off the disabled list on Sept. 1. "There's a little more life to everything, a little more finish to his pitches. He's done a nice job."

Colorado (60-83) won a series for the first time since Aug. 24-26.

Seattle appeared to be on the way to tying the game when Seager lined a one-out pitch from reliever Jairo Diaz down the left-field line with a runner on first in the eighth. Barnes hustled over and made a fully-extended, diving catch to rob Seager of the hit. Seattle baserunner Ketel Marte, who had been on first, was all the way around second when Barnes made the incredible catch, and he couldn't beat the relay throw from shortstop Cristhian Adames -- resulting in the inning-ending double play.

"I wanted to give it everything I had because it was borderline fair-foul," Barnes said after getting an ice pack wrapped to the left side of his rib cage in the visiting clubhouse. "When you get that close to diving head-first into the wall, it's never fun, but I knew I had a little bit of room, so I went for it."

Colorado catcher Dustin Garneau had the best view of Seager's fly ball down the line, and he initially thought it would go foul.

"Then it straightened out," Garneau said, "and (Barnes) came out of freaking nowhere and dove."

"That's a game-changer," Weiss added. "That's the game right there."

Axford struck out American League home run leader Nelson Cruz to open the ninth, then he bounced back from a Robinson Cano single to retire the final two batters. Seattle right fielder Seth Smith hit a deep fly ball to center for the final out of Colorado's one-run victory.

Colorado third baseman Nolan Arenado, who went 1-for-12 in the series, had the Rockies' lone RBI. Smith drove in both Mariners runs with a bases-loaded single in the fourth.

Seattle starter James Paxton returned to the mound for the first time since May 28 but couldn't get an out after the third inning. He was pitching pretty well until allowing a leadoff double and a walk to start the fourth, leading to McClendon making a change. Paxton (3-4) allowed two hits and three runs -- two earned -- on 66 pitches over three-plus innings. He walked three and struck out four after being activated from the disabled list earlier in the day.

"I imagined he would be somewhat rusty," McClendon said. "His pitch count got to him pretty quick, and we had to go out there and get him."

The Mariners have now lost 75 games for the season, matching the total they had over 162 games in 2014.

NOTES: Colorado went into Sunday's game with a 6-26 record against left-handed starters. Seattle had LHP James Paxton on the mound. ... Paxton was officially activated before Sunday's game, 3 1/2 months after he was placed on the 15-day disabled list with a strained middle finger on his left hand. Paxton was making his first start since May 28. ... Rockies SS Jose Reyes (sore Achilles tendon) wasn't in the lineup for any of the three games in the Seattle series. ... The Mariners still haven't won a home series against the Rockies since 2001. Colorado's only visit to Seattle since then came in 2006, when the Rockies also took two of three from the Mariners. ... Colorado was scheduled to leave town after Sunday's game, destined for Los Angeles and a three-game series against the Dodgers that begins with LHP Clayton Kershaw on the mound for L.A. on Monday. The Mariners will host the Los Angeles Angels on Monday. ... Seattle CF Brad Miller was a last-minute scratch due to neck spasms. James Jones started in his place.