ST. LOUIS -- Max Scherzer walked with his head down as he made the slow trek from the mound toward the dugout, exiting the game during a still ongoing seventh inning that should have been over long before. He was on the cusp of polishing off his best outing since returning from the injured list, nearly finishing the seventh inning to keep the Nats within a run.

With two outs in the inning, however, Juan Soto lost a fly ball in the sun, allowing Paul DeJong to reach second base on a double and giving the Cardinals an opening for the three-run inning they rode to a 5-1 victory in Wednesday’s series finale at Busch Stadium.

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Tommy Edman punched a run-scoring single into right field to drive in DeJong. And then Scherzer hung a 2-2 curveball on his 109th pitch to Matt Wieters, his former batterymate for two seasons in D.C., that Wieters pounced on for a two-run homer. It spoiled what had been one of Scherzer’s best outings in months, as he finished with 11 strikeouts and no walks, but was charged with five runs on seven hits in 6 2/3 innings.

“I’m accountable for the pitches I throw,” Scherzer said. “Today, they put some good at-bats against me, and they were able to capitalize when they needed to in some big situations when the game was on the line.

“That’s what happens when you play playoff-quality teams. It comes down to the little stuff, so it doesn’t matter how good the big stuff is. Everyone can execute the big stuff at this point. It comes down to the fine details. That’s what kind of did me in today.”

Scherzer was frustrated after the game, although he downplayed the impact of Soto’s mistake in left field. Soto was wearing sunglasses on the play and appeared to be tracking the routine fly ball, which had an expected batting average of just .020 according to Statcast, before he lost the ball in the sun on the way down.

“I was trying to let the ball go outside of the sun, like try to be on the other side,” Soto said. “But I got there too late. And that just happens.”

Still, this was an encouraging step forward for Scherzer, the first time since July 6 -- before he ever made a trip to the IL this season -- that he reached double digit strikeouts, a feat that was once almost routine. For five consecutive starts from June 14-July 6, Scherzer recorded double digit strikeouts in each of them.

His performance was not enough to settle the slumping Nationals, losers of 10 of their past 16 games, who are clinging onto the top slot in a tight National League Wild Card race. Washington leads both Chicago and Milwaukee, who are tied for the other Wild Card spot, by 1 1/2 games after both teams lost later Wednesday night.

“Frustrating,” said bench coach Chip Hale, who is filling in as manager for Dave Martinez. “We know where we are, we know we’re in the fight. Max was throwing great. He had his good stuff today, felt good, felt good late in the game.”

With the NL Wild Card picture becoming so crowded suddenly, the Nationals may no longer have the luxury of holding Scherzer back to start a potential win-or-go-home game. Currently, Scherzer is in line to make his final regular season start in Game 162 against the Indians at Nationals Park, a game that is increasingly likely to have major playoff implications. Looking ahead, the Nationals decided to shuffle their rotation for this weekend to make sure Stephen Strasburg would also be lined up to start a potential Wild Card Game on regular rest if needed.

On Wednesday afternoon, Scherzer looked much closer to the ace the Nationals will need to make a deep postseason run. He retired 12 of the first 13 batters he faced, yielding only a solo homer to Edman in the third inning on a cutter outside of the strike zone. Scherzer benefited from a slight mechanical adjustment that helped him control his body and added life on a fastball that topped out at 97.6 mph.

Not much has gone right for the Nationals lately, but Scherzer’s gigantic step forward Wednesday is among the top reasons they can remain optimistic.

“For me, all the pitches were really playing up today,” Scherzer said. “And I like where my stuff is at.”