ST. PETERSBURG -- Before Saturday’s game, Brendan McKay sat in the home clubhouse by his locker, which is conveniently located between those of Blake Snell and Tyler Glasnow. The highly touted left-hander checked his phone and appeared calm, just three hours before taking the mound for the first time in the Major Leagues.

McKay was greeted by some teammates as Snell answered questions from the media in his scrum one day before his start. McKay listened to the Rays’ ace, and then changed into his uniform and began to prepare himself for his turn on the mound.

With his mom, dad, both sisters, girlfriend and other friends and family in attendance at Tropicana Field, McKay stepped out on the field about 40 minutes before first pitch. He stretched for a few minutes out in right field before grabbing his tan glove with his name stitched in blue and moving over to the bullpen mound to work with pitching coach Kyle Snyder and catcher Travis d’Arnaud. That’s when it hit McKay that he would be making his Major League debut.

“It just takes you back, and you take a deep breath and just mellow yourself out and get to it,” McKay said.

Once McKay got through his warmup pitches, he joined the rest of the bullpen for the traditional high-five line. Five minutes later, McKay led the Rays back out onto the field to become just the fifth left-handed starter to debut in franchise history, and the first since Snell on April 23, 2016. At 4:10 p.m. ET, Tampa Bay’s No. 2 prospect delivered a 94 mph fastball to Shin-Soo Choo, and the McKay Era was underway.

• Box score

And what an impressive beginning it was. The southpaw went on to retire the first 16 hitters he faced, tossing six scoreless innings to lead the Rays to a 5-2 win over the Rangers. McKay allowed one hit and one walk, and he struck out three.

“It was fun to watch,” said Rays manager Kevin Cash. “The way he carried himself, it was kind of unflappable. You would not have thought, if you just picked up and turned on the TV, that that was his first Major League start. He picked us up in a big way.”

McKay lost his perfect game bid with one out in the sixth inning on a Danny Santana blooper into right field. The fans responded with a standing ovation.

“It gave you chills in the moment,” McKay said. “It shows that the crowd knows that something special is going on and they respect it.”

The 5 1/3 perfect innings to start a game is a new franchise record for a pitcher making his Major League debut. Jeremy Hellickson previously held the record after retiring 10 straight to open his career in 2010. It’s also the second-longest perfect game bid in a debut since 1961, and tied with Ken Cloude for the longest in the American League.

“The minute he showed up, he was locked in,” d’Arnaud said. “I’m sure it was the moment he was waiting for his whole life. He was as cool as a cucumber. He knew what he needed to do; he knew what kind of pitcher he was when I was talking to him about what he liked doing. That was a lot of fun.”

In the first inning, McKay established control of the inside corner against right-handed hitters and the outside corner against left-handed hitters, and he was able to maintain consistency throughout the outing. The Rays gave him a cushion with a three-run second, capped by Avisail Garcia’s two-run homer.

McKay’s first career strikeout came against likely All-Star Joey Gallo in the fifth inning. McKay opened the at-bat with back-to-back curveballs for strikes to get ahead in the count. After throwing a ball up in the zone to change Gallo’s eye level, McKay came back with a 94 mph fastball on the outside corner to get Gallo swinging.

It’s the type of sequence that shows why he was tabbed as the top pitching prospect in the Rays’ organization. d’Arnaud said that the command McKay showed on Saturday reminded him of reigning National League Cy Young Award winner Jacob deGrom.

“Not only does he have 95 [mph] in his back pocket, but he’ll put it where he wants to,” d’Arnaud said. “He’s so smart that when he sees you cheating, he knows how to pitch to that.”

McKay threw 81 pitches, 55 for strikes. His fastball topped out at 95 mph and he mixed up his curveball, cutter and changeup to keep Rangers hitters off-balance throughout the afternoon.

But perhaps the most impressive aspect of McKay’s debut was the composure he showed. Even when Texas got two runners on in the sixth inning, McKay stuck with his game plan and struck out Delino DeShields swinging. That calm demeanor has excited the entire Rays organization ever since they selected the two-way player with the No. 4 pick in the 2017 Draft out of Louisville.

“You could tell early on -- you could see him kind of taking deep breaths, and you could see he was kind of anxious, but he looks like a pretty calm guy out there,” said Rangers manager Chris Woodward. “He's not a real high-energy guy, but you can tell he definitely competes, and he did a good job against us.”

The left-hander is scheduled to pitch again against the Yankees on Thursday, and then the Rays will make a decision on whether to keep him in the Majors or send him to Durham. But Saturday was a good indicator that McKay could pitch at this level.

“It helps you know that it’s there,” McKay said. “You aren’t doing anything different or trying to do too much or changing what you do.”