Magneuris Sierra secured the first bunt hit of his big league career to start off the 10th against Kelvin Herrera, laying one down the first-base line. Miguel Rojas followed with a bunt of his own, reaching on obstruction by catcher Spencer Kieboom.
Home-plate Tim Timmons told a pool reporter: "I had obstruction because the ball was not in the immediate area of the plate. The runner was obstructed. It wasn't clear whether Herrera was going to field the ball, or the catcher. The catcher can field the ball, but he can't obstruct the runner and clear the runner out of the way."
Brian Anderson blooped a single to right, loading the bases for Realmuto, who took a 2-1 fastball the other way, sending a fly ball high down the right-field line. The Nationals had elected to use five infielders, moving Bryce Harper to first base to try and nail the go-ahead runner at the plate. With just two outfielders, the pop fly was able to fall.
"He put it in play," Marlins manager Don Mattingly said. "J.T. put it right where the two outfielders couldn't get to it. It was one of those, when it goes up, you're like, 'I don't think it's deep enough.' Then you realize they don't have anybody over there."
It marked Realmuto's third walk-off hit of his career -- his first since a walk-off home run against the Mets on Sept. 19, 2017 -- and Miami's seventh of the season. Realmuto also accounted for the Marlins' first run of the night, scoring on a Yadiel Rivera sacrifice fly in the fourth after earning a walk from Gio Gonzalez.
The Nationals had won the first two games of the four-game series by a combined 19-4 margin, and eight straight at Marlins Park.
"Obviously, to get a win like that against these guys, you don't think one is really going to hold up," Mattingly said. "When we get to the ninth, you're like, one might hold up. Obviously, it was good to get a win there against a team like that that's been beating up on us."
MOMENTS THAT MATTERED With two outs and runners on second and third in the ninth, the Nationals were poised to take the lead. Michael A. Taylor ripped a 2-2 slider to the hole, but Rojas laid out, making the diving stab on his glove side and firing across the diamond to keep the game knotted at 1.
The Marlins would not have needed Rojas' stellar play, however, if closer Kyle Barraclough was able to shut the door earlier in the inning.
Barraclough plunked Harper's back foot with an errant slider and Ryan Zimmerman followed with a base hit. Two batters later, Daniel Murphy rolled a 2-1 fastball through the right side, scoring Harper and tying the game at 1.
Barraclough, who is being scouted by contending clubs as a possible trade piece, has now blown saves in his last two opportunities. He surrendered a walk-off grand slam to the Rays on Sunday.
"When he gets in trouble, it's when he's not getting ahead in the count," Mattingly said. "I was glad to see him kind of regroup, get out of that, and keep the game tied there."
After earning National League Reliever of the Month honors for his astounding June, the right-hander has been a different pitcher in July. In 11 appearances, Barraclough is 0-2 and has an 8.38 ERA -- that's nine earned runs, 16 hits and three homers in 9 2/3 innings.
RICHARDS FINDING A GROOVE He has flown a bit under the radar, but of late, Trevor Richards has been the Marlins' best pitcher, and the numbers prove it.
In Richards' last five outings, the rookie is 1-0 with a 2.30 ERA. In those 27 1/3 innings, the right-hander has allowed just seven earned runs and struck out 28.
"It's just been going after hitters a little bit more than we were at the beginning," Richards said, explaining the changes he has made of late that have led to such success. "Being able to attack. My fastball command has been better. It starts from that and being able to hit spots and then mix speeds off of that."
Saturday was arguably Richards' best start of his young career. He went six scoreless innings, allowing just three hits and two walks while punching out eight.
The highlight of Richards' dominant performance was without question the effectiveness of his changeup. Of his 91 pitches, 32 were the circle change. Not only was his offspeed inducing swings and misses, making Nationals hitters look foolish at times, it also consistently led to weak contact. According to Statcast™, the average exit velocity on six changeups hit in play was 80.8 mph.
Richards' battery mate Bryan Holaday put it bluntly in regard to the changeup: "It's disgusting."
YOU GOTTA SEE THIS If you weren't already aware, Sierra is fast. Very, very fast.
The rookie's bunt single in the 10th inning showcased his elite speed. According to Statcast™, Sierra was clocked at a breath-taking sprint speed of 31.0 feet per second.
"I had that in my mind going up there to the plate, and then I took a glance over to first and I saw the first baseman playing deep," Sierra said via an interpreter, on his idea to lay down a bunt. "I knew I had the ability to get it down, and I wanted to take advantage of the opportunity. I got it down."
To put that number into perspective, the league average is 27 feet per second, and it's considered to be "elite" if you can get to 30.
Further, it took the rookie outfielder a mere 3.46 seconds to go from home-to-first. That's the fastest time recorded since Statcast™ began tracking in 2015, faster than anything during Dee Gordon's tenure in Miami.
"I've just got to play the game that I know. I'm not a Barry Bonds-type hitter," Sierra joked. "I've got to stick to what I'm good at."
HE SAID IT "I've been waiting for a while to do it. Any time you can help your team win, it's got a good feeling attached to it. Especially for the first time, it'll stick out in my mind for a long time, and I'm definitely appreciative for it." -- Marlins rookie Brett Graves, on his first career win. The right-hander pitched a perfect 10th inning.
UP NEXT The Marlins send Jose Urena to the mound to conclude their four-game series with the Nationals at 1:10 p.m. ET on Sunday. It will be Urena's team-leading 21st start of the season. The right-hander has struggled at home of late, as he hasn't won a game at Marlins Park since Sept. 20, 2017, the longest such streak in franchise history. Jeremy Hellickson goes for the Nationals.