It was a weekend to forget for the Mets.

Sunday afternoon’s 9-0 loss to the Tampa Bay Rays at Citi Field marked the Mets’ most lopsided defeat of the year and capped the first series in which they’ve been swept this season.

Tampa Bay once again took advantage of walks and capitalized on Mets miscues, while hard-throwing Rays starter Shane Baz dominated.

“They beat us in all aspects of the game,” outfielder Brandon Nimmo said.

The Rays scored the game’s first three runs in the second inning against Mets starter Griffin Canning, despite hitting only one ball out of the infield.

After Canning walked the inning’s first two batters, Rays speedster José Caballero laid down a well-placed bunt. Third baseman Brett Baty initially stepped toward third base before fielding the ball, allowing Caballero to reach and load the bases.

The Rays then scored on Kameron Misner’s RBI force out; a wild pitch by Canning; and Danny Jansen’s RBI single.

“Walks. They get a bunt down. We don’t make a play. Before you know it, we’re down three,” manager Carlos Mendoza said. “We just didn’t play well.”

Canning was tagged for six earned runs in 4.1 innings. The right-hander issued a season-high five walks, marking the third time in five starts he walked at least four batters.

It was only the second time this season — and the first in 38 games — that a Mets starter surrendered more than four earned runs.

“I’m just falling behind guys, walking guys, probably shying away from contact too much,” said Canning, who fell to 6-3. “It’s a good lineup, a hot team right now. You just can’t give them free bases.”

The Mets trailed 4-0 in the third when Pete Alonso came up with the bases loaded and two outs. But Baz struck out Alonso with a high, 99-mph fastball to extinguish the scoring threat.

Alonso had reached base in 22 consecutive games, but that streak came to an end Sunday as the slugger went 0-for-4 with two strikeouts and a double play.

The Mets finished 0-for-7 with runners in scoring position and stranded 12 baserunners.

“We made a few mistakes — defensive, pitching and hitting — but they played really well,” Nimmo said. “Sometimes, you’re gonna run into that, where the other team’s playing really well and you’re not playing your best.”

Equipped with an overpowering fastball, Baz recorded six strikeouts and limited the Mets to three hits over 6.2 innings.

The Rays put the finishing touches on Sunday’s rout when 21-year-old phenom Junior Caminero drilled a three-run home run off Ryne Stanek in the ninth.

Jared Young, a Mets position player, then came in to pitch and recorded the final out of the ninth. By then, many within a sellout Father’s Day crowd of 42,804 had already left.

“You hate to get swept here at home, but you’ve got to move on,” Mendoza said.

The Mets (45-27) had not been swept since a three-game series in Seattle last August, nor had they lost a game by more than six runs this season.

They entered the series against the Rays with a 27-7 record at home — the best start in franchise history.

But Tampa Bay (39-32) won Friday night’s series opener, 7-5, behind a six-run sixth inning, then won Saturday’s game, 8-4, on the strength of a five-run fourth. On Saturday, the Rays turned a pair of errors by Mets pitchers into four unearned runs.

“There’s 162 [games],” Mendoza said. “You’re gonna go through stretches where this is gonna happen. Obviously, we have to play better. We didn’t execute, we didn’t play clean baseball, and they made us pay.”

The three-game losing streak matches as a season-long for the Mets.

This one came at an inopportune time, as the second-place Philadelphia Phillies swept the Toronto Blue Jays over the weekend, cutting their deficit in the National League East behind the Mets to 2.5 games.

“You try and take it for a learning moment,” Nimmo said of the sweep. “People will look at this series and see if there’s a recipe on how to beat us, so I definitely think there’s something to learn from it, but at the same time you try to not make it bigger than it is. We’ve been very good to this point.”

The Mets will look to rebound during a six-game road trip against a pair of division rivals. They begin a three-game series in Atlanta on Tuesday, then go to Philadelphia for another three-game set.