ST. PETERSBURG -- The Rays knew it would feel strange to see Zach Eflin in black and orange.

For a year and a half, Eflin was a veteran presence in the Rays’ clubhouse and a reliable anchor in their starting rotation. This season, he was their Opening Day starter and most experienced player. Then, two weeks ago, he was gone -- dealt to the division-rival Orioles for three prospects during a dizzying week of trades that reshaped Tampa Bay’s roster.

"If there's one word that was going to sum it up," Brandon Lowe said, "'weird' is going to be the one."

It turned out to be as difficult as it was weird for Tampa Bay’s scuffling lineup. Eflin pitched seven scoreless innings against his former team in his return to Tropicana Field, and the Orioles dealt the Rays a 4-1 loss in the series opener Friday night.

• 'It's like a video game': Eflin dominates former squad in return

“Unfortunately, we've seen that quite a bit out of him,” Rays manager Kevin Cash said, “and it happened against us.”

Eflin allowed only four hits and a walk while striking out seven. He has won each of his first three starts with the Orioles, pitching to a 2.33 ERA in his new uniform.

“It's always interesting when you face someone like that, that you spend so much time around and catch,” Rays catcher Ben Rortvedt said. “You know what he has, but also, you know what he's trying to do. It's a fun battle. He came out on top, but it's always a fun battle.”

The Rays didn’t get a runner to second base against Eflin until the fifth inning, when Taylor Walls singled and stole second. Their lone extra-base hit off him was José Caballero’s two-out double in the seventh. Dylan Carlson broke up Baltimore’s shutout bid in the ninth, launching his second home run for the Rays down the right-field line off reliever Yennier Cano.

“[Eflin] was obviously pretty sharp. We saw a lot of that over here as well,” Rays starter Zack Littell said. “It's a tough night.”

It’s been that kind of stretch for the Rays, who have lost five of their last eight while averaging 2.9 runs per game. Friday’s defeat dropped their record to 58-57 and left them five games behind the Royals for the final American League Wild Card spot.

The Rays’ up-and-down play to this point, which has left them around .500 all year, was one reason they made the difficult decision to deal veterans like Eflin prior to the Deadline. Eflin told reporters Friday night he appreciated the front office’s transparency, and that he was “made aware that something might go down” before he was traded.

“I have so much respect for that clubhouse and everybody that works for this organization, so it was really cool to step on that mound again and be able to face them on the other side,” Eflin said after the game.

Still, he said, coming back to face his former team exactly two weeks later “was kind of like an out-of-body experience.” After signing the largest free-agent contract in franchise history, Eflin went 21-15 with a 3.72 ERA in 50 starts for the Rays and finished sixth in last year’s AL Cy Young Award voting.

Beyond what he did on the mound, he made deep connections with his teammates and left a strong impression on Tampa Bay’s younger players.

"He meant a lot. Just a great dude, a great friend, mentor, person to have in the clubhouse,” outfielder Josh Lowe said. “I definitely took a lot from him and will always be grateful for my time playing with him and the friendship that we've made."

With Eflin dealing, Littell could hardly afford to make any mistakes. He didn’t make many, but the Orioles’ relentless lineup still scratched across three runs during his five innings of work. Colton Cowser hit his second career leadoff home run during a 30-pitch first inning, but Littell recovered and quickly worked his way into the fifth, only to find more frustration.

After giving up a leadoff single and another base hit on a ball misplayed by second baseman Christopher Morel, Littell struck out Cowser and retired Anthony Santander. He thought he caught Gunnar Henderson looking at strike three, only for it to be called ball four, then surrendered a two-run single on a 69.4 mph bloop to center by Ryan O’Hearn.

“They're a team that fouls balls off until they get that mistake. It's what good lineups do,” Littell said. “It can be frustrating at times, but I thought I did a nice job just not giving in in those moments. It just didn't go our way there at the end.”