Nick Pivetta returned to Boston’s starting rotation last week, providing depth to what has been a surprising strength. John Bazemore/Associated Press

A quarter of the way through the Major League Baseball season and the Red Sox are still hanging around in the American League East.

Entering play Monday against Tampa Bay, the Sox were third in the division at 21-19.

So what to make of this team? Boston is 14-4 against sub-.500 clubs but just 7-15 against teams with winning records.

Hovering around .500 will keep you in contention for one of the three wild-card berths, but it won’t help you get to the top of the toughest division in baseball.

The AL East is stacked, and the Sox really haven’t had much of a chance to compete against division foes. Just how they fare in those division games will be pivotal in a playoff push.

The Sox entered Monday 0-3 in the division, getting swept by the Orioles earlier in the year. Boston gave up 23 runs in three games against Baltimore, a stunning number for a pitching staff that has given up just 3.5 runs per game this season.

The three divisional games played is far and away the fewest of any team in the East. Furthermore, in all of MLB, only the White Sox have played fewer division games.

That all changed Monday, when they began a series against the Rays. Boston will play 10 of  its next 16 games against AL East opponents, including seven against Tampa Bay.

It’s been a tough first quarter of the season for Kevin Cash’s Rays, who have been outscored by 32 runs this season. Are the Rays a good team?  Are they anything like the team that won 99 games last season, the second-most in the American League?

It’s been a roller-coaster season for Tampa Bay, which went 2-8 from April 21-May 5. As always, the Rays can pitch. They struggled on the mound during that tough stretch but rebounded with an AL-best 2.25 ERA in the seven games that followed.

As for the Sox, their pitching continues to stun the baseball world. They lead all of MLB with a 2.75 ERA. No other team began the week with an ERA below 3.00. More impressively, Boston’s starting rotation has posted an MLB-best 2.45 ERA.

They’ve done it with injuries to 80% of their projected rotation, although some players are returning to the mix. Nick Pivetta and Brayan Bello returned last week, and Garrett Whitlock will make a rehab appearance in the coming days. That has led to difficult decisions, like sending Josh Winckowski back to Triple-A Worcester.

Winckowski was one of the most important pitchers in the bullpen last season, but his ERA was nearly half a run higher this year. He had shown promise as a starter (1.69 ERA in three starts) but the Sox want him to work on perfecting a third pitch in the minors.

“The message is, ‘go down there and work,’ ” said Manager Alex Cora. “Like I said, you know, we’re more talented than last year, and there’s gonna be tough decisions. And there’s more tough decisions coming up. Over the last five years, man, the message is a lot easier now, you know, for us to be good, we have to be better.”

Cora will face another tough decision in the coming days. If all goes well, Whitlock could be starting for the Sox by next weekend. That could push Cooper Criswell back into the bullpen – or to the minors. The Sox are 5-0 when Criswell starts.

For the past couple of years Cora has talked about needing to have starting pitchers ready in Triple-A. Winckowski and Criswell could provide that depth.

And it’s the depth that could keep the Sox surprising people as the season progresses.

Tom Caron is a studio host for the Red Sox broadcast on NESN. His column appears in the Portland Press Herald on Tuesdays.