Red Sox reliever Marcus Walden retired all seven batters he faced during Boston’s 6-5 victory over the Colorado Rockies on Wednesday night. Associated Press/Rick Scuteri

BOSTON – Michael Chavis got credit for the walk-off hit on Wednesday night, the first for the rookie.

Marcus Walden might as well have put the ball on a tee for him, that’s how crucial the reliever was to the Boston Red Sox’s 6-5, 10-inning victory over the Rockies. Making a crucial contribution is getting to be old hat for Walden.

His seven-up, seven-down relief appearance began with two outs, one on and the score tied in the seventh ended and ran through the ninth inning.

The 30-year-old righty struck out four Rockies, mixing in his four-seam fastball, slider and cut fastball when he wished and getting big swings and misses when needed.

The biggest came with that first out, when he struck out Raimel Tapia to strand the go-ahead run at second base.

“Which is definitely something new for me,” said Walden about getting those swings and misses or weak contact – the three non-strikeout outs were infield popups and a groundout. “The biggest thing is just keeping the ball on my side of the plate, on what I’m trying to do, not leave anything over the heart of the plate, so if we’re burying cutters into lefties or sliders down and in, trying to keep it there. Obviously I still missed a couple spots today but fortunate with Tapia on the high slider, he swung through it. Trying to command the ball and keep it on my side of the plate.”

This kind of performance is not a one-and-done for Walden.

Quietly Walden is becoming the dominant, go-to reliever for the Red Sox this still-young season. Since April 20, he has appeared in 10 games and over 16 2/3 innings he has struck out 19 and walked one. He has allowed one run.

He has pitched in the middle of games and more recently, later and later in more and more clutch situations.

And, like Wednesday night, he is pitching in multiple innings.

Seven of his 15 appearances this season have been for two or more innings.

“It’s just trying whenever I get the ball,” Walden said. “I’ve got no problem taking it in the third after Hector or taking it today in the seventh with a guy on base. Just still trying to go out there and pitch, it really doesn’t matter what inning it is, honestly, I’m trying to go out there and get three outs.”

And while the Red Sox didn’t score for Walden in the bottom of the seventh, eighth or ninth innings and give him the win he deserved, his output certainly was valued.

Manager Alex Cora was thrilled.

“At this level, you don’t want contact late in games,” Cora said. “Waldy, with Tapia, the first hitter, it was kill slider, slider until he swings and misses. That’s the way it is. That’s the way it works at this level now. That’s why everybody likes bullpens. You don’t want contact. If there’s contact, it’s a fly ball or a weak ground ball. There’s not, like, try to induce him into a double play.

“His stuff is playing great at this level right now. The slider is good, the cutter is good, the fastball up is great. He was amazing today. We put him in a situation, tie game, and he gave us more than enough to have a chance to win a game.”

Chavis won the game in the end.

And he couldn’t have done it without Walden.

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