Jordan Zimmermann leads the Nationals with a 2.45 ERA. (Jonathan Newton/WASHINGTON POST)

One of the supposed truths about this Washington Nationals team was that their starting pitching would be something not to rely upon, but to overcome. The front office spent the winter whiffing on would-be aces. Several more months of sweat and toil separated Stephen Strasburg from a major league mound. The Nationals were left with five pitchers who shared in common the fact that few other teams would slot them into the top three places of their rotation.

Liván Hernández, Jordan Zimmermann, John Lannan, Jason Marquis and Tom Gorzelanny have instead formed perhaps the most consistent — and, 15 games in, one of the best — starting rotations in the major leagues. Nationals starters have compiled a 3.30 ERA, fifth-best in the majors, and they are the only team to have received at least five innings every game from their starting pitcher. Rather than bringing down the Nationals, the rotation has allowed them to overcome a slumping offense and take an 8-7 record with them as they begin a six-game trip Tuesday in St. Louis.

It is, of course, awfully early to go making proclamations about how effective this rotation will be for the next 147 games. “I’ve seen a lot of guys pitch good in April,” one Nationals official said. “Once they start getting guys out in July, then I’ll be impressed.” But the rotation’s start to the season has so far mocked convention and silenced the scouts and pundits who predicted doom for the Nationals’ starting five.

“We kind of took that upon ourselves to show some people how good we really are,” Zimmermann said. “People didn’t think our starters were that good. We’re going to go out, give it our all and see what happens.”

Last year, even with 12 starts from Strasburg, the Nationals’ rotation ranked among the worst in most every important statistical category. Their biggest sin was a lack of stamina mixed with an abundance of calamity. The Nationals threw more innings than only one team, the Pittsburgh Pirates. Twenty-four times, the Nationals’ starter failed to pitch more than four innings, including six of the first 15 games.

This winter, Nationals pitching coach Steve McCatty placed a phone call to each of his starting pitchers. He told them to come to spring training prepared to throw three innings in their first start of spring, one more than usual. McCatty wanted not only to enhance his starters’ endurance, but also set a tone.

McCatty knew his rotation would not blow away opposing lineups, but he expected it to pitch deep into the game, to at least give the Nationals a chance to win. The extra inning in spring training emphasized the theme.

“I think,” Hernández said, “it’s the best idea.”

For the first 15 games, the Nationals’ starting pitchers have left with the Nationals tied, ahead or trailing by two runs or less. They have done it by listening to McCatty’s other theme for the season, which he summarized thusly: “Throw strikes, Meat.”

Every pitching coach in the world tells his pitchers not to walk anyone, but it has been a special emphasis for McCatty. He pitched for the Oakland Athletics teams managed by Billy Martin in the early ’80s, and he recalls often one of Martin’s truisms: “The only play we can’t defense is a walk.”

Aside from Zimmermann and Gorzelanny, the Nationals’ rotation relies primarily on sinkerballs and weak contact, a strategy foiled by walks. Nationals starters have walked only 2.1 batters per nine innings, third in the league. Despite striking out just six batters per nine innings, Nationals starters own the eighth-best strikeout-to-walk ratio in the majors.

Early-season results can serve to deceive, but the strikeout-to-walk ratio is perhaps the most telling underlying stat. If Nationals starters continue to not allow walks, they should be able to continue to defy their preseason critics.

“I don’t care what they’re saying,” McCatty said. “They have been good. Everybody can go back to the same thing — why are they not good? Because they don’t throw 96 [mph]. And that’s what everybody is judging this rotation on, is by the velocity of the pitches. To me, it’s if you throw strikes. It’s great when you have the staff that [the Phillies] have. They’ve got real good guys. We have good guys, too. But they’re different. They’re different sort of pitchers. But I’m not surprised. I really am not.”

The Nationals’ rotation has been carried not by one pitcher, but by a collective, day-in-day-out effort. Zimmermann leads the Nationals with a 2.45 ERA, 15th in the National League. But all four qualifying Nationals starters rank in the top 25, something no other NL team can say.

In 13 of 15 games, the Nationals’ starting pitcher has allowed three or fewer earned runs. Nationals starters have produced a quality start — at least six innings, three earned runs or less – in seven straight games, and they have allowed one or two earned runs six games in a row.

The consistency has bred more consistency. While the four starters who aren’t pitching a given game support their fellow starter, they also think of ways to one-up their teammate.

“We’re pretty much just feeding off each other,” Zimmermann said. “When one guy goes out and goes six innings, you want to go out and do a little better than that. It’s just kind of a snowball effect.”

Said McCatty: “It gives you confidence. You always want to do a little bit better than the next guy.”

Do that enough, one day after the next, and some expectations start to fade away. The Nationals starters knew what the baseball world expected of them, and they have shown they don’t care.

“We’ve got a great group,” Hernández said. “People don’t think this team can do nothing. We’re going to surprise a lot of people.”