When Paul Skenes made his MLB debut last May, the Pittsburgh Pirates knew that coming up behind him was another wave of promising pitching prospects inching closer to the big leagues in Braxton Ashcraft, Bubba Chandler and Thomas Harrington.

Less than a week into the regular season, Harrington became the first of the three, all of whom are ranked by MLB Pipeline as top-10 prospects in the Pirates’ system, to make his major-league debut.

Harrington, the Pirates’ No. 3 prospect, chosen 36th overall by the club in the 2022 MLB Draft, was called up Tuesday to start against the Tampa Bay Rays at George M. Steinbrenner Field.

Facing Shane Baz, a 2017 first-round pick by the Pirates, Harrington pitched four innings, allowing six earned runs in a 7-0 defeat.

The 23-year-old Harrington, who was charged with the loss, gave up seven hits, walked four and struck out a pair while throwing 54 of his 90 pitches for strikes.

“I think I learned I’ve just got to execute a little bit better,” Harrington said on the SportsNet Pittsburgh postgame show. “I put myself in some good counts, didn’t execute and got hurt from it. These guys are really good hitters. I’ll learn from it and get better next time.

“Regardless of the results, it was a great day for me and my family.”

Offensively, it was another quiet night for the Pirates.

Baz (1-0) delivered six scoreless innings, allowing seven hits while striking out a career-high 10.

The Pirates struck out 15 times in total, managing nine hits, zero of which were for extra bases.

Before Harrington had a moment to soak in his MLB debut, the Rays had a man aboard in the bottom of the first, as Yandy Diaz singled on the first pitch Harrington threw.

Harrington then walked Brandon Lowe on seven pitches before Junior Caminero advanced both runners with a flyout.

Then, the red-hot Jake Mangum, who was 4 for 4 Monday against the Pirates (1-5), put the Rays up 2-0 with an RBI double into left field.

Mangum soon came around to score via a Kameron Misner RBI single, making it 3-0 Tampa Bay.

Harrington walked another before the end of the frame, but on his 30th pitch, he finally escaped, striking out Taylor Walls.

“I think in the first inning, he got sped up, a little bit of jitters,” manager Derek Shelton said. “He settled back down. I think the one thing we know about Tommy is he has the ability to execute his breaking balls and the changeup, and today, it just didn’t look like he had it.

“That happens sometimes in your first start. We know he has good stuff. Just need to settle him down and make sure he gets in the zone.”

After Harrington rebounded with a 12-pitch second inning, the Rays took a 4-0 lead in the third off a Misner sacrifice fly, plating Mangum, who got aboard with an infield single.

Mangum had advanced to second when Harrington walked Curtis Mead and took third on a wild pitch.

In the fourth, the Rays went up 6-0 courtesy of a two-run homer by Lowe.

The Pirates’ offensive struggles this season continued, as they offered Harrington zero run support.

An inning-ending double play by Tommy Pham in the fourth spoiled back-to-back hits by Bryan Reynolds and Oneil Cruz.

In the fifth, Ke’Bryan Hayes and Jared Triolo got aboard, but the Pirates were unable to bring either of them around to score.

“We had some situations where we had runners at first and second, nobody out, runners at first and second, one out, and we just couldn’t get a ball to get through,” Shelton said. “We’ve got to get some balls in the gaps and right now, we’re just not getting any of those.”

Following Harrington’s exit, Justin Lawrence, Caleb Ferguson and Joey Wentz threw scoreless innings in relief.

The Rays added a final run in the eighth off Dennis Santana to take a 7-0 lead.