DENVER — Even the Dodgers’ most trusted reliever can make mistakes.

Blake Treinen came in with the score tied in the bottom of the eighth inning and but gave up a solo home run to Connor Joe that gave the Colorado Rockies a 3-2 victory over the Dodgers Saturday night at Coors Field.

“It was a surprise,” Dodgers manager Dave Roberts said of the shocking nature of Treinen getting beat. “I was actually kind of thinking about who was going to take down the next inning with the score being tied. But yeah, I’ve got a ton of trust in Blake and he left a cutter out over.”

Treinen struck out the first two batters in the eighth and had Joe (a Dodger farmhand in 2018 and 2019) down 1-and-2 when he left a 91-mph cutter over the heart of the plate. It was a pitch selection Treinen and catcher Austin Barnes both second-guessed later, though Treinen said the “poor execution” was “my fault.”

“It’s not like it’s a bad pitch if I execute it, but that was pretty flat middle-middle and there are definitely better pitches to throw in that situation,” Treinen said. “Of all the pitches that I could’ve thrown, that was probably the one pitch that gives him the most chance.

“Me and Barnes talked about it and we both shook our heads like ‘Why did we do that?’ Baseball sucks sometimes. … One bad pitch kinda cost me and it cost the team.”

Treinen might have been protecting a lead instead of a tie if the Dodgers’ offense were living up to its billing.

Through 18 innings at Coors Field — its reputation being sullied by the Dodgers’ hitters thus far this weekend — the Dodgers have put up 15 zeroes, scoring five of their seven runs in the first two games in one inning Friday night.

“I thought (Rockies starter German) Marquez was really good. In my opinion, he’s one of the top pitchers in baseball,” Dodgers manager Dave Roberts said. “I thought he mixed well tonight, used his slider, more change(ups) than usual and obviously a plus fastball. So we really didn’t get too many good swings off him.”

Marquez might not be recognized around baseball as one of the top pitchers in the game. But the Dodgers have reason to hold him in high esteem.

The Rockies right-hander held them to three hits over seven innings Saturday, striking out five and getting 10 outs on ground balls — all unaffected by the altitude in Denver.

In 12 career starts against the Dodgers, Marquez has been a problem they have yet to solve. He has a 2.89 ERA in those 12 starts and held the Dodgers to a .209 batting average despite the challenges of his home field.

“He’s got a quick arm. His fastball gets on you,” Barnes said. “Then his slider especially here — it’s a bunch of different sliders. Sometimes it’s a true slider, a little sweeping and sometimes it cuts a little. He’s tough. He always pitches us tough.”

Barnes was the only one to get the better of Marquez. He worked a seven-pitch at-bat in the third inning, got a full-count fastball in and drove it 453 feet into the left-field seats — the Dodgers’ only home run of the season so far and the longest of Barnes’ career.

The Rockies scored first against Dodgers starter Tony Gonsolin — and almost didn’t score that run.

After singles by Kris Bryant and Brendan Rodgers put two runners on, Ryan McMahon hit a top-spin one-hop liner to Mookie Betts in right field. Bryant tried to score from second base but Betts’ throw beat him home. But Dodgers catcher Austin Barnes lost control of the ball as he put the tag on Bryant.

Barnes made up for it two innings later when he worked a seven-pitch at-bat against Marquez and got a full-count fastball over the inside part of the plate. Barnes turned on it and sent it 453 feet into the left-field seats for a solo home run — the longest of Barnes’ career.

That stands as the Dodgers’ only home run two games into the season and one of only three extra-base hits they have had at baseball’s most accommodating venue.

“I don’t know the answer to that,” Roberts said of the offense’s slow start. “I liked the at bat-quality. Again tonight, I just thought Márquez would have done the same thing to any lineup out there.”

Tony Gonsolin and Tyler Anderson kept the Dodgers in the game and they tied it in the eighth.

Gavin Lux lit the fire, ending an eight-pitch at-bat against Colome with a solid single to right field. The Dodgers took a softer approach after that — Barnes dropped a single into center field (72.5 mph off the bat) and Mookie Betts tied the game with a pop single (69.9 mph) into the no-man’s land created by the big outfield expanse at Coors Field.

Freddie Freeman came up with a chance to create his first memory as a Dodger and nearly did. He drove a fly ball to the 415-foot mark in straightaway center field where Rockies center fielder Sam Hilliard hauled it in with his back to the wall.

Barnes was caught between second and third and did not make it back in time to tag up and advance on the play. That proved costly when Trea Turner chopped an infield single to third base, loading the bases instead of driving in the go-ahead run.

“With one out, by the book, you don’t (look to tag up) because you’re already in scoring position,” Roberts said. “But certainly on a ball that’s that far out, it wouldn’t have been a bad play. That’s something we’ll continue to learn from — to not concede third base certainly.

“As the book is written, whoever wrote the book, it’s a halfway with one out, but certainly if you can get back to tag and get to third base, it’s not a bad baseball play.”

Max Muncy flew out to strand the bases loaded, setting up Joe’s heroics in the bottom of the eighth.

“It felt awesome,” said Joe who overcame testicular cancer to return to the big leagues last July, five months after his original diagnosis. “Blake’s a really good pitcher. He’s got elite stuff.

“Fair to say it’s up there (as a career highlight) — top one or two.”