UPDATE (Tuesday, Sept. 18, 10:08 a.m.): Before Tuesday's game against the Boston Red Sox, the Yankees made it official, calling up Justus Sheffield, per Yankees PR:

Justus is served. 👏 pic.twitter.com/l2mrYNsOm8 — New York Yankees (@Yankees) September 18, 2018

Prior to today's game, the Yankees made the following roster moves:

Recalled

Signed

Transferred

NOTE: This post was updated Sunday morning with news that Sheffield's call-up is being delayed until Tuesday and Domingo German also will be joining the Yankees from Scranton/Wilkes-Barre:

NEW YORK -- A bad day at the ballpark led to a long-awaited dream come true for Yankees' No. 1 prospect Justus Sheffield.

His Scranton/Wilkes-Barre RailRiders lost the Governor's Cup to the Durham Bulls on Saturday with a 6-2 loss in Game 5 of the best-of-five International League championship series and Sheffield contributed to the disappointment with a poor relief outing. But his standout season overall trumped a bad final Triple-A performance of the season, as Sheffield was told after the game that he's being called up to the big leagues for the first time.

"I am still at a loss for words," Sheffield told the Wilkes-Barre Times Leader. "I'm super excited. I just can't believe it."

Along with righty Domingo German, Sheffield will join the Yankees on Tuesday for the start of their series at Yankee Stadium against the Boston Red Sox.

Why wait until Tuesday?

Sheffield and German both pitched Saturday, so they would be unavailable Sunday and Monday is an off day for the Yankees.

"This gives them a chance to pack up and get here (to New York) and get settled," Yankees manager Aaron Boone said Sunday.

According to MLB Pipeline, Sheffield is the Yankees' top prospect and the 27th best in the majors.

Sheffield was 7-6 with a 2.58 ERA this season in 25 outings, 20 as a starter, for Double-A Trenton and Scranton/Wilkes-Barre.

In the International League postseason, he was 1-0 with a 2.25 ERA in three relief outings, but he allowed six runs, two of them earned, on nine hits over five innings.

On Sunday, Sheffield relieved starter German in the third inning and immediately let two inherited baserunners score on a wild pitch and single. The next inning, Durham scored three unearned runs off Sheffield, who hit two batters and was tagged for a three-run double in the frame.

Sheffield still is viewed by the Yankees as a starting pitcher, but his first big-league stint will be as a reliever. He was a starter all season until late August when the Yankees began grooming him for a late-season call-up as a reliever. He did well coming out of the bullpen, pitching to a 1.35 ERA in five regular-season outings with 10 strikeouts and one walk over 13 1/3 innings.

"The transition to the bullpen, obviously, I knew there was something going on there," Sheffield said. "So it was hard for me to block it out and do my thing. When I did, I felt back to myself. It was one of those things where it was hard to block out."

Sheffield had been expected to join the Yankees on Sept. 1 when big-league rosters opened up, but the club instead opted to keep him in Triple-A for the RailRiders' playoffs and give lefty reliever Stephen Tarpley a first major league opportunity.

If Sheffield fares well in whatever opportunities that he gets with the Yankees in the final two weeks of the regular season, he may be able to pitch his way onto their postseason roster. Regardless, the Yankees think Sheffield will benefit just from being around for the final two weeks of the season.

"You hope that guys get the benefit of being around it and being a part of it, and hopefully they have an opportunity to impact us in some way and help us out in these final couple weeks," Boone said.

Randy Miller may be reached at rmiller@njadvancemedia.com. Follow him on Twitter @RandyJMiller. Find NJ.com on Facebook.