Big blow to SF Giants’ rotation: Alex Cobb placed on IL with oblique strain

Giants' rotation is back to 3 healthy starters with the loss of Cobb, whose 3.09 ERA was eighth-best in the NL.

LOS ANGELES — Just as the Giants’ number of healthy starting pitchers grew to four on Saturday, their rotation shrank back to three starters Sunday morning.

In a surprise move before Sunday’s series finale against the Dodgers, the Giants placed right-hander Alex Cobb on the 15-day injured list with a left oblique strain. Young right-hander Keaton Winn, who made his MLB debut this week in St. Louis and was already here on the taxi squad, was added to the roster in his place.

Cobb, 35, has been one of the majors’ most effective starters this season, teaming up with Logan Webb to form a formidable one-two punch. In 14 starts, including one complete game shutout, Cobb had a 3.09 ERA, tops in the Giants’ rotation and eighth-best in the National League.

It has been a tougher go of it for Cobb over the past month, with a 5.23 ERA over his past six starts.

Nonetheless, any injury is a significant blow to an already shorthanded rotation, particularly to one of its top two arms. Oblique injuries are notoriously tricky, meaning Cobb’s absence could be an extended one, depending on the severity revealed by an MRI.

The Giants entered the season with seven capable starters on their 26-man roster, but that number was down to three Sunday.

Alex Wood returned from his second stint on the injured list with five shutout innings in Saturday’s 15-0 win, joining Webb and Anthony DeSclafani as the Giants’ only healthy starters. Webb now is the Giants’ only starter to remain healthy and effective in the rotation for the entire season.

Ross Stripling is in the final stages of his rehab from a low back strain, but it remains a question how effective he can be after a rough start to the season. The Giants’ other free-agent addition, Sean Manaea, was also ineffective in the rotation to start the year but has been much better since being moved into a bulk role in the bullpen, similar to how the Giants are using Jakob Junis, another starting option entering the season.

With their shortage of starting pitching, the Giants have turned to bullpen games more frequently than they would like — two out of every five turns through the rotation — but that strategy also hit a snag this weekend, with John Brebbia, their go-to opener, expected to miss a significant chunk of time with a lat strain.

Winn and fellow rookie righty Tristan Beck have been starters throughout their minor-league careers and can take down multiple innings. Beck has been especially effective out of a bulk role recently, with a 1.00 in 18 innings over his past seven games, while Winn relieved Cobb in his last start, earning a save with four scoreless innings Wednesday in St. Louis, which puts him on the same schedule as Cobb.

At Triple-A Sacramento, of course, is 21-year-old Kyle Harrison, the top left-handed pitching prospect in the game. Harrison has a 3.42 ERA and 80 strikeouts but 37 walks in 14 starts this season, including a 1.74 mark over his past five outings while increasing his workload and cutting down on his walks.