"I knew I hit it good," he said. "But I was running hard."
Buck, who hit a grand slam on opening day, missed another by inches when the ball hit the top of the wall and caromed back onto the field. He settled for a three-run triple that helped the Marlins come from behind to win for the second consecutive night, this time by erasing a four-run deficit to beat Washington 7-4.
"I thought it was a home run," manager Edwin Rodriguez said. "But it was good enough."
Chris Coghlan had three doubles and a single and scored three times for the Marlins, and Omar Infante put them ahead to stay with an RBI single in the sixth. Four Florida relievers combined for four shutout innings.
But Buck made the biggest contribution. With Livan Hernandez trying to protect a 4-1 lead and two outs in the fifth inning, Buck fouled off two 3-2 pitches, then lofted a fly that landed near the 404-foot sign. With the ball ruled in play, the Marlins' 237-pound catcher chugged into third for his first triple since 2009.
"That might be the only way he'll get one -- hitting a ball off the wall that caroms around," teammate Chris Volstad said.
Rodriguez argued Buck's hit had cleared the wall, but the call stood after a replay review.
Washington's Ian Desmond, who entered the game 0 for 13, had four hits and two RBIs. But the Nationals, who began the night batting .121 (4 for 33) with runners in scoring position, went only 2 for 10 in those situations.
"We just have to keep putting them out there and finish it off," manager Jim Riggleman said. "With the energy and attitude on the bench, it pains them to have that happen the last couple nights."
The Nationals (1-4) have an overall average of .209, and they've scored only 14 runs.
"The season is just starting," Hernandez said. "You don't make the playoffs in four or five games."
The Marlins made several offseason moves to upgrade a shaky bullpen, and in the first two games of the series, their relievers have shut out Washington on three hits over 8 1/3 innings.
"Obviously the season is 162 games, but that's what we expect to do," Sanches said.
Josh Johnson, who has a career record of 7-0 against Washington, is scheduled to start Thursday when Florida tries for a sweep.
The Nationals' frustration peaked in the eighth. As reliever Todd Coffey left the game, he argued with plate umpire Todd Tschida and was ejected. Coffey then threw his glove and went face to face with Tschida.
"The situation dictates that I've got to be more composed and stay within myself and help the team," Coffey said, "and I didn't."
Hernandez took a 4-0 led into the fifth before tiring. He departed for a pinch hitter after throwing 97 pitches in five innings. He gave up six hits and five walks.
Coghlan came home when shortstop Desmond mishandled Hanley Ramirez's grounder for an error.
"You've got to play really good baseball to get back in a game like that," Buck said. "You've got to pitch well and hit well."
Volstad needed 95 pitches to get through five inning and left for a pinch hitter trailing 4-0. Volstad, who won all four of his starts against Washington last year, gave up four hits and four walks.
"Obviously it wasn't my best game," Volstad said. "But I was happy with the way I battled."
With his third walk-off hit in the past two seasons Tuesday, Marlins third baseman Donnie Murphy is tied for second in the majors during that span. ... Volstad twice retired Jayson Werth, who is 1 for 22 against the right-hander. ... Hernandez remained winless (0-3) in his past six starts against Florida.