Major League Baseball bullpens are often subject to unfair expectations by the fanbase.

Their successes are expected and their failures are magnified (especially if it’s late in the game). And most of the time, relievers are operating with very little margin for error.

The Cubs bullpen has come under a lot of fire from the fanbase this season, but they’ve quietly been one of the best groups in the league over the last month of action.

They had to shoulder a heavy load Thursday as starter Adbert Alzolay lasted just 3.2 innings but the relievers answered the call in a big way, allowing only 1 earned run in 5.1 innings.

“Yeah, it was nice. Setting those guys up, with Adbert not going really far, we got some really good innings out of the bullpen tonight and we needed that,” David Ross said. “Those guys continue to work and grow and continue to perform and that was nice to see tonight. Those guys did a really nice job.”

Since that impromptu weekend off in early August when the series in St. Louis was postponed, the Cubs relief corps has been a Top 5 unit.

Here’s where the Cubs bullpen ranks in baseball since Aug. 7:

ERA — 4 (3.42)
WHIP — 5 (1.23)
AVG allowed — 2 (.212)
OBP allowed — 4 (.301)
SLG allowed — 4 (.351)
K% — 2 (29.5%)
FIP — 3 (3.57)
xFIP — 1 (3.68)

They also rank in the middle of the pack (15th) in walk percentage (10.8%) in that same time frame.

After some early-season struggles, Ross is pleased with the progression by the bullpen.

“There’s been maybe a few bumps in the road along the way,” Ross said. “I think as a whole, they’ve done a good job. Guys are starting to command the baseball really well — some quick innings, throwing strikes. It’s been really nice to see.

“Seems like a different guy every night that throws the ball well. [Ryan Tepera’s] done a good job. Craig [Kimbrel] looked good [Wednesday] night; I thought he looked really sharp. obviously [Jeremy Jeffress] and [Rowan Wick], doing a good job. [Josh] Osich two out of three good outings. As a whole, we’re throwing the ball well from down there.”

As Ross mentioned, Kimbrel had a nice outing Wednesday night against the Reds. He gave up a single, but later picked that same runner off first base.

Kimbrel also etched his name in the Cubs history books, becoming the first reliever to strike out 2 or more batters in 9 straight relief outings — a single-season record. (Hippo Vaughn struck out 2 or more in 10 straight appearances, but it spanned multiple seasons — 1915-16.)

Over those last 9 outings, Kimbrel has a 2.16 ERA, with both runs coming during the loss in Cincinnati on Aug. 29. He has walked 7 but also racked up 19 strikeouts in 8.1 innings as his fastball velocity and movement continues to trend in the right direction.

Jeffress has been the anchor in the bullpen all season, boasting a 1.00 ERA to go along with 7 saves and 3 holds. Rowan Wick is 4-for-4 in save opportunities, leads the team with 4 holds and carries a 3.14 ERA.

Dan Winkler (3.07 ERA, 1.30 WHIP) has been solid while Jason Adam has pitched well (3.00 ERA, 16.0 K/9) while bouncing between South Bend and Chicago. Kyle Ryan has allowed a run in only 1 of his last 7 appearances.

Tepera has struggled a bit of late, but he’s missing bats (13.8 K/9) and was one of the team’s most reliable relievers for the first half of the season.

Duane Underwood Jr. is coming into his own and ascending into a more high-leverage role in the bullpen.

Plus, the Cubs pitching staff is on the verge of adding some reinforcements — all reports are positive on José Quintana, Tyler Chatwood and Andrew Chafin as they continue to work their way back from injury — which should only help to strengthen the bullpen.

With the postseason just over two weeks away, the timing is perfect for the Cubs relief corps to be putting it all together.