The Mets had made it easy to forget about the season's ebbs and flows. Things have clicked so well lately that a sellout crowd packed Citi Field expecting more of the same, a comfortable afternoon against a last-place team.

What they got instead was a reminder that foregone conclusions remain few and far between.

Now, after Saturday's 3-1 loss to the Red Sox, the Mets find themselves needing a victory in Sunday's series finale to avoid a sweep.

"Today we looked a little tired for me," manager Terry Collins said. "The back-to-back extra-inning games, the 3 o'clock in the morning getting back from Philly, all of the things that have gone on, we've been dragging a little bit."

Indeed, after enduring consecutive extra-inning games, the Mets went 0-for-7 with runners in scoring position and left five on base, extending a sudden streak of futility by an offense that has been scorching for most of the past month.

A crowd of 43,255 flocked to the park, drawn in by a pennant race and a bobblehead giveaway. It was the second-largest attendance figure in regular-season history at Citi Field, trailing only this year's Opening Day.

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The throng watched as Red Sox righty Joe Kelly outpitched 2014 NL Rookie of the Year Jacob deGrom, who bounced back from the worst start of his career.

In his fifth double-digit strikeout game of the season, deGrom (12-7) held the Red Sox to two runs in six innings and struck out 10. Kelly (8-6) struck out only two but limited the Mets to one run in 7 1/3 innings.

Red Sox third baseman Pablo Sandoval's RBI double in the sixth highlighted a two-run inning against deGrom.

Sandoval moved to third on Xander Bogaerts' lineout to center, and after a walk to Travis Shaw, first baseman Daniel Murphy elected to start a potential double play instead of throwing home to cut down Sandoval. Brock Holt beat the relay throw back to first and Sandoval scored uncontested.

"I kinda got caught in between there. That was the easiest way to describe it," said Murphy, who went 0-for-4.

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Mookie Betts smacked his 11th homer of the season off Hansel Robles in the seventh to give the Red Sox a 3-0 lead.

In the Mets' half of the seventh, Sandoval's diving stop of Wilmer Flores' grounder snuffed out a Mets rally that was confined to Juan Uribe's RBI double.

"He did a great job of executing pitches, keeping the ball down and throwing his breaking ball when he needed to," Travis d'Arnaud, who went 0-for-3 with a walk, said of Kelly. "He kept us off balance."

The Mets' National League East lead fell to 5 1/2 games when the Nationals beat Miami, 5-1, Saturday night.

The Mets wrapped up their road trip in Philadelphia on Thursday on a seven-game winning streak. They also concluded a 30-game stretch in which they went 22-8 with 55 homers.

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But after an 8-1 road trip through hitters' havens in Baltimore, Colorado and Philadelphia, the Mets have slumped since their return to Citi Field, enduring what Collins called "a blip."

For the first time since July 23 and 24 against the Dodgers, the Mets have gone two consecutive games without a homer.

In their last three games, the Mets have gone 3-for-31 with runners in scoring position. In that span, they have stranded 32 baserunners.

Said Murphy: "It's the ebb and flow of baseball."