With the defeat, the Reds lost possession of the third wild card spot, falling a half-game behind the Miami Marlins and slipping into a tie for fourth place in the wild card standings with the Arizona Diamondbacks.
Nevertheless, there is no reason the Reds can’t play their way into the playoffs.
They now enter the soft underbelly of their late-season schedule with 17 of their final 20 games against below .500 teams.
Three are in New York against the Mets. They may no longer have pitchers Justin Verlander and Max Scherzer, but they will have a mighty say on who gets the coveted third wild card spot.
In addition to three games with the Reds, the Mets have four games against the Marlins and four against the Diamondbacks.
And the contenders?
The Marlins have three against the Philadelphia Phillies, three against the Atlanta Braves, seven against the Milwaukee Brewers and four against the Mets.
The Diamondbacks have seven against the Chicago Cubs, two against the San Francisco Giants and those four against the Mets.
The Giants have seven against the Los Angeles Dodgers, three against the Houston Astros and two against the Diamondbacks.
Even the Cubs, who own the No. 2 spot in the wild card standings, have a rocky road — seven against the Diamondbacks, three against the Braves and three against the Brewers.
So if the Reds pay attention to their risky business, they could have an open path to the playoffs.
Richardson put the Reds in a 7-1 hole in his 4 2/3 innings.
After his teammates gave him a 1-0 lead in the first on TJ Friedl’s triple and Spencer Steer’s single, Richardson served up three long balls.
He walked Ty France with one out in the second and Michael Ford drove a two-run home run into the right field seats for a 2-1 Mariners lead.
Seattle struck for five runs in the fourth, an inning that began with a single by former Reds third baseman Eugenio Suarez.
It was his first hit in nine at bats during the three-game series and he stranded eight runners. He also doubled in the ninth.
Suarez scored on France’s double. Richardson walked No. 9 hitter Josh Rojas on a full count and J.P. Crawford ripped a three-run home run. One out later, Cal Raleigh unleashed his 26th homer, completing the five-run inning and giving the Mariners a 7-1 lead.
As they always do, the Reds didn’t pack away their bats for another day.
They tried to chip away.
They scored a run in the fifth on Will Benson’s second double, a single by Jake Fraley and Friedl’s sacrifice fly.
They scored another in the sixth on Elly De La Cruz’s walk, stolen base (his 26th) and a one-out single by Christian Encarnacion-Strand.
When Tyler Stephenson singled, Seattle starter Logan Gilbert was replaced by Matt Brash. He was greeted with a single by Noelvi Marte.
It was 7-3 and the Reds had the bases loaded with one out, one big swing from tying it.
But Benson struck out and Fraley grounded into a fielder’s choice to snuff the rally.
Seattle added a run in the seventh on a run-scoring single by France to make it 8-3 as the Mariners avoided getting swept for only the third time this season.
One at-bat too late, Benson homered, a solo shot in the ninth inning, for the final margin.
Seattle starter Gilbert was credited with his 13th victory and he is 5-0 over his last seven starts and 9-2 over his last 15 starts.
After taking Thursday off, the Reds open a three-game series Friday night in GABP against the last-place St. Louis Cardinals.
Cardinals at Reds, 6:40 p.m., Bally Sports Ohio, 700, 1410