Wilson Ramos singled to lead off the 10th inning, took third on a throwing error and scored on Ian Desmond’s fly ball as the Nationals improved to 12-4, continuing their best start since moving to Washington from Montreal in 2005. (Patrick McDermott/Getty Images)

Stephen Strasburg watched from the dugout Saturday afternoon as Ian Desmond walked into the batter’s box in the 10th inning. His victory had vanished after Brad Lidge made a hash of the ninth inning, but Strasburg never worried.

“There’s no sense of panic when we get to that situation,” he said later. “We know that if the guy up to bat doesn’t get it done, the next guy will.”

Less than a month into the season, the Washington Nationals have conditioned themselves, in the toughest moments, to expect victory. Desmond ended the Nationals’ 3-2 triumph over the Miami Marlins with a sacrifice fly in the 10th inning that gave Washington 10 wins in its last 12 games.

Even without the entire projected middle of their order, the Nationals clinched their fifth series victory of the season and joined the Texas Rangers and Los Angeles Dodgers as the first major league teams to reach 12 wins.

But with his second two-run, ninth-inning collapse in 10 days, Lidge torpedoed Strasburg’s shot at earning his third victory with his six scoreless innings, a performance that lowered his ERA to 1.08. Afterward, Manager Davey Johnson vowed to stick with a ninth-inning time share between Lidge and Henry Rodriguez.

The team improved its record in one-run games to 6-2. “I didn’t see any letdown on the ballclub,” Johnson said. “We hung in there.”

The Nationals won with a lineup that included veterans Mark DeRosa and Chad Tracy, signed as bench players, hitting third and fourth. Third baseman Ryan Zimmerman sat with mild right shoulder inflammation, first baseman Adam LaRoche had a day off and outfielder Michael Morse entered Day 10 of his six-week shutdown.

The Nationals’ starter gives the team a chance to win almost every game, no matter who is backing him. On Saturday, Johnson sent out Strasburg, the ace who has spent the season’s opening month taking his place among the best pitchers in baseball.

In less than a month, Strasburg has answered any questions about how he would pitch in his first full season after Tommy John surgery. In four starts this year, all Nationals wins, Strasburg is 2-0 with 25 strikeouts and six walks over 25 innings.

Saturday, Strasburg matched Marlins right-hander Anibal Sanchez pitch for pitch, the zeros mounting for both teams until the sixth inning. Strasburg allowed four hits and a walk while striking out six, five on his curveball.

In the bullpen before his second start in New York, Strasburg made an adjustment with his curve. He needed it Saturday as the Marlins hacked at fastballs early. Thirty-four of Strasburg’s 94 pitches were off-speed.

Strasburg tried to ignore the score as the 0-0 tie continued. “It’s only a matter of time to where the bats are going to break loose,” he said.

In the sixth, Desmond broke the deadlock. He annihilated Sanchez’s 2-0 hanging cutter, smashing it roughly 10 rows behind the visitor’s bullpen in left field.

Desmond entered the year as a question mark — could he lock down the leadoff spot and assert himself, in his third season, as an everyday shortstop? Less than a month into the season, Desmond has been perhaps the Nationals’ most valuable position player. He’s hitting .294 and playing shortstop at a Gold Glove level.

“What a difference a year makes,” Desmond said. “Last year, this time of the year, it was a huge struggle. I had eight errors. I was hitting about .200. We weren’t really winning. This year, it’s a new year. It’s a fresh start, which is nice. I’m feeling good about it.”

Jayson Werth, who boosted his average to .322, added a solo home run in the seventh inning — his first homer this season — to give the Nationals a 2-0 lead. Ryan Mattheus and Sean Burnett combined to preserve the game into the ninth inning, when Johnson summoned Lidge.

Lidge walked leadoff hitter Hanley Ramirez — “the mistake of the inning,” Johnson said — then left a 90-mph fastball over the plate to Logan Morrison, who crushed a two-run, game-tying homer into the upper deck in right field.

“Right now, I’m not throwing well out there,” Lidge said. “My location’s bad.”

Still, despite Rodriguez having yet to allow an earned run, Johnson said he would split the closing duties between the two until Drew Storen returns around midseason. “I still like Brad Lidge,” Johnson said. “I’ve got a game plan and I’m going to stay with it.”

Lidge’s implosion only led to Desmond’s chance. Wilson Ramos led off the 10th with a rocket single to center off reliever Edwin Mujica. LaRoche, pinch-hitting, followed with a groundball down the line to first baseman Gaby Sanchez, who botched the play twice. He didn’t step on first base before throwing to second, and his throw sailed high and trickled into center field, allowing Ramos to scoot to third.

Up came Desmond, who had watched Mujica throw first-pitch fastballs outside. Desmond expected the pitch, but he fouled off inside heaters to fall behind, 0-2. “He beat me twice,” Desmond said. “At that point, I just tried to grind.”

Desmond took one ball, then clobbered a fly ball to center field. When center fielder Emilio Bonifacio fired the throw back into the infield wide of home plate, the Nationals’ dugout emptied to celebrate another win that didn’t come easily.

“That’s the big thing,” Strasburg said. “It’s finding a way.”