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ST. LOUIS — The Mets’ hits total over two games Sunday suggested they should have won both, but an inability to finish business flipped the equation.

Mostly, they floundered with runners on base.

First, the Mets fell short of a comeback by leaving the bases loaded and the tying run at third over the final two innings in a 6-5 loss to the Cardinals in Game 1 of a doubleheader.

In the nightcap, they wasted plentiful chances in the middle innings in a 5-4 loss in the series rubber game.

The Mets lost for the fourth time in five games in dropping a second straight series.

The Mets had 10 hits in each of the games and left 12 and 10 runners on base, respectively, in the two losses.

In the nightcap, Tylor Megill slogged through five innings in which he allowed four earned runs on four hits and three walks with six strikeouts.

After the Mets rallied for a 4-2 lead with four runs in the third inning, the Cardinals tied it against Megill in the bottom of the frame.

Lars Nootbaar and Masyn Winn walked before Nolan Arenado and Willson Contreras each delivered an RBI single.

Arenado’s grounder — generously ruled a single — could have easily been the inning’s third out, but Mark Vientos bounced a throw past Pete Alonso, bringing in the run and extending the inning for Contreras to deliver.

Juan Soto was denied a three-run homer in the fourth when Victor Scott II reached above the center field fence to rob him.

The Mets left the bases loaded in the inning.

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Max Kranick was tagged for the go-ahead run in the sixth on Scott’s RBI double.

Alec Burleson’s two-run homer in the second put the Mets in a 2-0 hole before they sent nine batters to the plate in the third in building their lead.

Alonso singled in a run before Starling Marte delivered a two-run single and Francisco Alvarez’s grounder through the right side brought in a fourth run.

Blade Tidwell had a shaky major league debut in Game 1.

In addition, Jesse Winker departed with what the team termed right side discomfort.

Winker, who started in left field, has served as the team’s primary DH this season.

Winker was set to receive an MRI exam on his oblique before Sunday’s second game.

Over 3 ²/₃ innings Tidwell surrendered six earned runs on nine hits and three walks with two strikeouts.

He was removed after throwing 82 pitches.

Tidwell said he needed to execute better ahead in the count.

The Mets rallied in the eighth and ninth innings, but each time left the tying run in scoring position.

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In the eighth they scored twice before leaving the bases loaded.

Overall, the Mets were 3-for-15 with runners in scoring position in Game 1.

Alonso and Brandon Nimmo delivered successive two-out doubles in the first inning to produce the game’s first run.

Contreras tied it 1-1 with a homer leading off the second on a slider.

The Cardinals threatened with two additional base runners in the inning before Tidwell escaped by striking out Nootbaar.

Winker’s sacrifice fly put the Mets ahead 2-1 in the third, following Juan Soto’s leadoff single and Alonso’s second double of the game.

Alonso reached third on a passed ball but was left stranded.

Tidwell surrendered three straight singles to load the bases in the third before Nolan Gorman’s sacrifice fly tied it 2-2.

The Cardinals knocked out Tidwell in the fourth.

Burleson walked to load the bases, Donovan stroked an RBI single and Arenado walked.

Contreras followed with a two-run single that placed the Mets in a 6-2 hole and ended Tidwell’s afternoon.

Jeff McNeil walked leading off the sixth and following Luisangel Acuna’s single scored on Francisco Lindor’s RBI fielder’s choice.

But with a chance for the Mets to get closer after Lindor reached second on Jose Barrero’s throwing error, Soto was caught looking at strike three in a second straight plate appearance, concluding the threat.

Lindor’s two-run single in the eighth against Phil Maton got the Mets within 6-5.

But the Mets left the bases loaded in the inning, as Alonso struck out in an eight-pitch at-bat against lefty JoJo Romero and Nimmo was retired.

In the ninth, Vientos singled leading off against closer Ryan Helsley, but the pinch-runner Marte was left stranded at third base.