Reliever Zack Kelly delivers a pitch in the ninth inning of the Boston’s 7-2 loss to the White Sox on Sunday in Boston. Kelly gave up five earned runs in the ninth inning. Steven Senne/Associated Press

It was always the bullpen.

Red Sox fans got an ugly reminder Sunday that Boston didn’t have enough relief pitching to get to the promised land this season. Sox relievers have the highest bullpen ERA since the All-Star break. It was a glaring problem in the ninth inning when relievers gave up five runs to one of the worst teams in the major league history. The 7-2 loss to the Chicago White Sox was another dagger to Boston’s hopes of a late-September surge.

The Fenway faithful booed heartily as the White Sox ran up the score late and ran off with just their 33rd win of the season. Zack Kelly gave up five hits and five runs in the inning and gave away any good vibes that had been built up with wins over the lackluster White Sox on Friday and Saturday.

Had the Red Sox been able to finish the sweep, they would have started the week three games back of the slumping Twins, who lost three straight to Kansas City over the weekend, for the third AL wild card. Boston turned to a 24-year old pitcher as a way to give its rotation extra rest, and Richard Fitts delivered with an impressive big-league debut.

Fitts, one of the three pitchers acquired from the Yankees for Alex Verdugo, never pitched above Double-A prior to this season. On Sunday he limited Chicago to six singles over 5 2/3 innings. It continued a good run of starting pitching for Boston, which has a 2.33 ERA from its rotation over the last two weeks.

Fitts’ impressive showing was more proof that the Red Sox got the better of their December trade with the Yankees. In addition to Fitts, the Sox got Greg Weissert – an important part of their middle relief group – as well as 23-year old Nicholas Judice, a 6-foot-8, 230-pound right-hander who is wrapping up his first pro season.

Verdugo is struggling for the Yankees, hitting just .235 with a .651 OPS and is in danger of losing his job to Jasson Dominguez, the star prospect called the Martian because of his out-of-this world potential.

Despite Verdugo’s struggles, the Yankees sit atop the AL East as they get ready for a four-game set with Boston later this week.

The Red Sox are hoping what they saw from Fitts is a glimpse into his future as a starter. Boston has been looking to rebuild the rotation for the past few years and hopes some of the pitchers who spent this season in Worcester are ready to answer the call.

Fitts held the White Sox scoreless for five innings. They finally got on the board in the sixth, scoring two unearned runs after a Triston Casas error.

The miscue was Boston’s major-league-leading 104th of the season. It has given up 88 unearned runs, the most in baseball. The inability to field the ball has led directly to multiple losses. Who knows where the Red Sox would stand with just league-average defense?

The defense has been horrendous, yet the Sox were still in a position to win if the bullpen could keep Chicago’s anemic offense from adding any runs. It couldn’t, and the team missed another chance to creep closer to the wild-card pack.

“We’ve just got to win,” Manager Alex Cora said before Sunday’s game.

Despite taking 2 of 3 games to win the series, losing on Sunday was another step closer to the end. There are less than three weeks remaining and the Red Sox would have to win about two-thirds of their remaining games to have a chance to make it.

Meantime they face two series against teams that are already making plans for October. After wrapping up this series with the Orioles, the Sox head to the Bronx for a four-game set with the Yankees. Tanner Houck is skipping a start because the Red Sox said he didn’t recover as well as he should have after the last start.

The news isn’t what the Red Sox want to hear in these final weeks. And the results aren’t what fans want to see. In the ninth inning on Sunday, those fans let their opinion be heard loud and clear.

Tom Caron is a studio host for the Red Sox broadcast on NESN.