SEATTLE — Aaron Cook expected he would be ready to rejoin the Red Sox after the All-Star break, the team having scheduled a series of rehabilitation starts for him at Triple A Pawtucket.

Those plans changed when Clay Buchholz landed in the hospital with a case of esophagitis. Cook was called up to face the Atlanta Braves last Sunday at Fenway Park and pitched five solid innings in a game the Sox won, 9-4.

With Buchholz on the disabled list, Cook remains in the rotation and will pitch against the Mariners Friday night.

Cook threw 79 pitches against the Braves and felt he had more left.

“I felt really good. Recovered a lot better that I thought I was going to,” Cook said Thursday. “I feel like we’re definitely building up and going in the right direction. Hopefully I can go there this time and try and push seven, eight innings.”

Manager Bobby Valentine thought that start was a good step for Cook.

“Considering he’s still finishing up a rehab, he was able to throw enough pitches to progress from the last time he pitched,’’ Valentine said. “He threw pitches up in the zone that had enough sink on them to still be effective and he maintained all his pitches through the 79 pitches that he threw. If he can build on that, I like what we have.”

It has been an odd season for Cook. The 33-year-old righthander, who has dealt with shoulder problems for several years, started the season in the minors so he could build up arm strength. When he made his debut with the Sox May 5, he was spiked while covering home plate and suffered a deep gash in his left knee.

Starting two major league games in a row is a bit of an accomplishment.

“It is nice to be healthy and taking the ball every fifth day,” said Cook. “I’m having a lot of fun.”

Other than spring training, Cook has never faced the Mariners. Only Chone Figgins, Miguel Olivo, and Brendan Ryan from that team have faced him.