BOSTON -- Six days after Kutter Crawford stifled the Mariners on just one hit over five scoreless innings, the righty learned what a fine line there is between success and struggle at the highest level.

On Saturday night at Fenway Park, facing a tough Cardinals lineup, Crawford was on the hook for six hits (including two towering homers) over four innings in an 11-2 loss for the Red Sox.

In what turned out to be a two-start stint in the big leagues while Garrett Whitlock and Nathan Eovaldi are battling back from injuries, Crawford was told after the tough outing he is being optioned to Triple-A Worcester.

“There’s work to be done, and we’re going to get after it,” said Crawford, Boston’s No. 24 prospect as rated by MLB Pipeline.

What did Crawford learn from the extremes of the past two starts?

“That I need to command all five of my pitches,” Crawford said. “I need to get my splitter in the zone more often to keep hitters honest with the ball moving the other direction versus everything going away. That’s cutters, sliders and just moving the fastball inside and outside and not just staying on one side of the plate.”

A lineup as strong as the one the Cardinals have will jump on a young pitcher who isn’t commanding, and they did.

Crawford saw that in real time. After retiring the first two batters in the first inning, Crawford gave up a single to Paul Goldschmidt. Up next was Nolan Arenado, who hammered a 3-2 cutter that was middle-middle over the Green Monster.

In the fourth, Nolan Gorman unloaded on a changeup that caught too much plate and deposited it a Statcast-projected 440 feet over the wall in center.

“He showed some flashes of good stuff. The four-seamer played today,” Red Sox manager Alex Cora said. “The cutter was OK. The breaking ball wasn’t there. So, that’s a good lineup. It seems like they were hunting certain pitches. Seemed like the four-seamer gave them trouble. Everything in between, they were on it.”

Seattle felt like a long time ago by the time Crawford came out of Saturday’s game.

“I needed to move my fastball around a little bit more in order to keep hitters honest,” Crawford said. “I think the big thing was not being able to command the secondary pitches as well as I did in Seattle.”

Cora: 'Robles needs to be ‘more aggressive’
Despite Crawford’s tough night, the Red Sox were right in the game, down just 4-2 when he departed.

But the bullpen got roughed up for six runs in a game-turning top of the sixth.

Hansel Robles took the brunt of the damage, giving up four runs on two hits and two walks while recording just one out.

Cora went out to check on Robles with a team trainer at one point during the inning.

“He’s fine. He kept moving his arm," Cora said. "I don’t know if you guys noticed it, but anyway, obviously he was coming back from [back spasms] 10 days ago. We just wanted to make sure everything was fine, and he said [it was].”

A big factor down the stretch for the Red Sox last season, Robles hasn’t been nearly as consistent this year.

“Hansel, on and off,” said Cora. “We’ve got to get him to be more aggressive in the zone. Throughout the season, the walks have been a factor. Last year, he didn’t do that toward the end, mid-August to September. Obviously the velocity isn’t 97, 98 like last year, but it’s still good enough to attack hitters.”

Davis preserves 'pen
The lone bright spot of Saturday’s defeat?

Lefty Austin Davis helped preserve the bullpen for Sunday’s rubber match against the Cardinals when he threw a career-high 56 pitches and matched a career-high of three innings. Davis pitched the seventh through the ninth, preventing Cora from having to bring in a position player.

The performance came on the heels of Davis getting roughed up Friday when he came on with a 6-1 lead and forcing Cora to bring in closer Tanner Houck.

“It’s one of those that, it’s a fine line, trying to get to 27 outs [from pitchers] or getting the last three with a position player,” said Cora. “But you’ve got to give him credit. He understands the game, and he didn’t feel right about what happened yesterday, not finishing the game, and he just wanted to finish. I’m glad that he got it done and he saved a few arms in the bullpen.”