BOSTON -- The rumor is that the Red Sox’s rotation is depleted by injuries. Actually, it is true. Nick Pivetta (right elbow flexor strain), Garrett Whitlock (left oblique strain) and Brayan Bello (right lat tightness) all remain on the injured list.

But you would never know it from the results.

Cooper Criswell, signed as a free agent on a modest $1 million deal last December, is the pitcher who is best embracing the next-man-up mentality.

In a marvelous performance on Tuesday night at Fenway Park, Criswell faced one batter over the minimum in his five scoreless innings, allowing two hits and a walk while striking out four in the Red Sox’s 4-0 victory over the Giants.

This was the second consecutive outing that Criswell (2-1, 1.65 ERA) went five innings and didn’t allow a run.

“It feels good,” Criswell said. “Any time you can go out and contribute and help the team win, obviously that feels good.”

In this age of overpowering velocity, Criswell’s hardest of his 79 pitches on Tuesday was 89.6 mph.

“He just located well, and maybe when he made the mistake, we didn't take advantage of it,” said Giants third baseman Matt Chapman. “I think he was putting the ball where he wanted to for the most part, keeping guys off-balance, and we weren't really able to get anything going. I think he's got good stuff -- obviously it's not the jump-off-the-chart fastball power stuff, but he still knows how to command the baseball and keep guys off-balance, and that's just as tricky.”

What did the Red Sox see that other teams didn’t when they signed the 27-year-old who had a 5.97 ERA in parts of three seasons on Dec. 13?

“This,” said manager Alex Cora. “I mean, just a guy that can pitch. He has pitchability. He throws strikes. He can move the ball around. It doesn’t always have to be 96-97 [mph]. There's certain guys that, with the movement and obviously where they go with their pitches, keep hitters off-balance, and that's what he does.”

At the end of Spring Training, Criswell wound up coming in sixth in the battle for the Red Sox’s five-man rotation. He started the season at Triple-A Worcester but was needed in Boston due to attrition by April 13, and he has been playing an important role ever since.

“He was good,” said Cora. “Really good. He went east/west. He kept them off-balanced, got some swing and misses. He was good in Spring Training and he’s been good for us. He threw the ball well in Worcester. This was the plan, you know, when we decided to go with the five guys. At one point, he was going to be part of this. We know how it works. I'm pleased that he's here doing his thing, and he'll be ready for his next one.”

It seems that everything new Red Sox pitching coach Andrew Bailey touches turns to gold. As the calendar flips from April to May, Boston’s starting rotation leads MLB with a 2.00 ERA. Tuesday’s shutout gave the club the MLB lead with six.

Could anyone -- even the Red Sox -- have predicted this?

“We expect to be consistent,” said Cora. “I know that every single night, we feel very comfortable where we’re going to be pitching-wise. Obviously, the numbers speak for themselves. But for me, this is not because of what we did in April. I felt very comfortable in Spring Training. We pitched well in Spring Training, all the guys.

“I can’t recall somebody that struggled, and it's a testament of the program, it’s a testament of the guys putting in the work. I think [catchers] Reese [McGuire] and [Connor Wong], they did an amazing job in Spring Training having a lot of conversations, and we're doing a good job.”

Considering all the injuries to the pitching staff and the position players, Boston (17-13) has to be viewed as one of the best early-season surprises.

“We're playing good baseball,” Cora said. “It’s one month out of the season and we still have a long way to go, but we’ve just got to keep continuing doing the things that we’re preaching. We’re playing better defense, we’re running the bases better. The offensive is going to be better. The pitching is going to be consistent. Win the series tomorrow and continue to roll.”