By Peter Abraham, Globe Staff

SEATTLE — Aaron Cook spent the better part of two seasons with a sore right shoulder, the former All-Star getting hit so hard so often that the Colorado Rockies didn’t bring him back.

The Red Sox gave Cook a chance and little else, inviting the 33-year-old to spring training as a non-roster player. New pitching coach Bob McClure had worked with Cook in the Rockies organization and vouched for him. But there were no guarantees.

“I’m a positive person, but my shoulder was a mess the last couple of years,” Cook said. “You wonder if you’ll ever get it back.”

On Friday night, Cook was the best he has ever been in a 5-0 victory against the Seattle Mariners.

Cook allowed two hits — both singles — and struck out two without a walk. He faced 28 hitters and threw just 81 pitches, 58 for strikes.

Short of a perfect game, it was about as efficient as a pitcher gets. Or maybe better. When Philip Humber of the White Sox threw a perfect game against Seattle on April 21 at Safeco Field, he needed 96 pitches.

“That’s as good as I’ve seen him,” Sox right fielder Cody Ross said. “What an unbelievable game.”

Cook, making only his third start of the season, threw first-pitch strikes to 19 hitters and got to a three-ball count once. Seattle never advanced a runner past first base. Cook’s heavy sinker helped produce 15 outs on the ground.

“He had his sinker going from the first pitch of the game. He was throwing it over the heart of the plate and they were swinging at it and putting the ball in play,” manager Bobby Valentine said. “The defense was doing everything he needed behind them. That was a great performance.”

Cook was even more composed afterward, recounting his memorable performance with barely a hint of excitement.

“It means a lot to go out there and prove that I’m where I want to be, where I was trying to, to be a effective pitcher and give out team a chance to win games,” he said.

“It’s definitely really satisfying. I think every pitcher, when they take the mound, they want to go out and throw a complete game and throw a shutout. To go out and do it, it definitely means a lot.”

It was the third career shutout for Cook, his first since 2009. The Red Sox backed him with four home runs.

The Sox have won five of their last seven and 10 of 13. At 41-36, they are now 5½ games behind the Yankees in the American League East.