When it comes to the Marcus Stroman trade, Saturday was a double-whammy for the Mets.

Anthony Kay allowed just two runs in 5²/₃ innings in Toronto’s 5-3 loss to the host Tampa Bay Rays, who have now won nine out of 10 games. Kay, one of the two pitchers the Mets traded to the Blue Jays on July 28 for Stroman, gave up four hits and three walks while striking out an impressive eight batters.

The 24-year-old left-hander left with a 3-2 lead and a chance to win the game, but another former Met, Travis d’Arnaud, and Daniel Robertson drove in runs with two out in the eighth inning to spark the Rays’ comeback win.

“It hasn’t sunk in fully yet,” Kay said. “Just having my friends and family here, I think, makes it the most special. It was really cool.”

Blue Jays manager Charlie Montoyo was impressed.

“He’s a bulldog on the mound. He pitches inside, he changes speeds. He did a great job,” Montoyo said. “Eight strikeouts against a good lineup. He was awesome. I wanted to say ‘wow’ and he was wow.”

Kay also said took a dig at the Mets after the game, saying the Blue Jays have given him more freedom with his pitching, whereas the Mets pushed him much harder to make changes after tough outings.

“I feel like when I was in Syracuse with the Mets they were trying to change too many things because I had a couple rough starts,” Kay told reporters after the game. “Once I got traded… (Toronto) told me to just do my thing.”

As for Stroman, he has struggled since coming to New York, and Saturday night was no exception. The veteran right-hander was touched up for five runs — four earned — in just four innings in the Mets’ 5-0 loss to the Phillies at Citi Field.

It was the fourth start at home for Stroman, a Medford native, and he has yet to thrive. He is 1-2 with the Mets with a 5.05 ERA and has been the weak link in the Mets’ rotation during their playoff push.

Making matters potentially worse for the Mets, Simeon Woods Richardson — the other pitcher the Mets gave up in the deal — could be an even better prospect than Kay, scouts told The Post’s Kevin Kernan.

The 18-year-old right-hander went 3-2 with a 2.54 ERA in 28¹/₃ innings with Dunedin, the Blue Jays’ Single-A team. It’s a marked improvement from the numbers Woods Richardson put up with Columbia, the Mets’ Single-A affiliate in which he was 3-8 with a 4.25 ERA in 78¹/₃ innings.

— with AP