ST. PETERSBURG -- On Thursday afternoon, veteran center fielder Kevin Kiermaier predicted the Rays’ four-game series against the Yankees at Tropicana Field would be “exciting,” “fun” and “challenging.” Those three words have defined this American League East rivalry over the past few years, and this season figures to be no different. But a few things had changed since these clubs most recently met.

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At the end of last season, the Rays had already clinched their second straight AL East title and were putting the finishing touches on a 100-win campaign. This year, the Yankees have put together the Majors’ best record, and they entered the series with a 4 1/2-game division lead.

“You find out a lot about your team when we need to rise to the occasion at the most crucial time,” Kiermaier said. “We know our work is definitely cut out for us, but this will be a really good test for us here in mid-May.”

Their first matchup of the season showed just how tough a test it’ll be all year. A few mistakes on the mound and an error by shortstop Taylor Walls shifted the momentum firmly in the Yankees’ favor in the sixth inning, and the Rays couldn’t recover against left-hander Nestor Cortes as they lost, 7-2, to fall a season-high-tying 5 1/2 games behind New York.

“We obviously understand they’re a really good team, but we also like where we’re at right now. It’s just one game. We still have three games to go in this series, 18 more in the season series,” left-hander Ryan Yarbrough said. “You’re not going to win all 19. We understand it’s going to be a battle, but just kind of erase it and move on to tomorrow.”

For five innings, though, the clubs looked evenly matched. Cortes was cruising on his way to an eight-plus-inning, one-run gem, but Yarbrough traded zeroes with him in the early going. Yarbrough finished the fifth inning having allowed only one walk while striking out five on 67 pitches.

“It looked like he had everything going, really,” manager Kevin Cash said.

Then things unraveled in a hurry for the Rays, who saw just how quickly the Yankees can capitalize on their opponents’ mistakes.

Yarbrough began the sixth inning by hitting Matt Carpenter with a full-count cutter. Marwin Gonzalez ended Yarbrough’s early no-hit bid with a clean single to center, then Aaron Judge smacked a 2-1 cutter for an RBI single. With two outs, two runners in scoring position and reliever Ryan Thompson on the mound, Miguel Andújar slapped a grounder to Walls at shortstop.

Walls fielded the ball cleanly, but he stumbled as he tried to stand. Walls said he simply lost his footing, with his toe sliding longer than he anticipated. That cost him valuable time to make an inning-ending play and pulled his momentum away from where he needed to make the throw. As a result, his throw skipped on the dirt past stretching first baseman Harold Ramirez, allowing both runners to score.

“I've just got to make a better throw,” said Walls, a slick-fielding shortstop by trade who has committed seven errors in his first full season as a utility infielder. “I've been giving the first basemen really tough plays to try to pick them in the dirt. Granted, they're not easy plays to begin with, but they're throws that I'm extremely capable of making, I'm used to making. Just haven't made them the past few nights.”

Just like that, the Yankees had a 3-0 lead. The way Cortes was pitching, that seemed all but insurmountable.

“I felt like that play kind of changed the complexion of the game a little bit,” Cash said.

“It’s a team where you can't make mistakes like that. Any little thing that they capitalize on, especially with the guy they had on the mound tonight, it's going to be tough to battle back and get runs,” Walls added. “Any small mistakes like that, or anytime they put runs on the board, especially when we're facing a guy like that, it's going to be tough.”

While the Yankees tacked on four more runs in the final three innings, the Rays had no answers for Cortes, who baffled Tampa Bay’s entirely right-handed lineup with cutters and four-seam fastballs as he worked into the ninth inning for the first time in his career.

“He was just commanding all of this stuff,” Rays catcher Mike Zunino said. “He was able to get some righties sped up, had great control of that cutter today and just made great quality pitches when he needed to.”

The Rays will play the Yankees 18 more times this season, with nine matchups in their next 25 games. Thursday was a reminder of what they’re up against, but they were hardly concerned afterward.

“You've just got to tip your hat. That team's very beatable, and we know we can beat them,” Walls added. “We're here. We're going to be here all year. There's [18] more games. We're going to be here.”