Tommy Milone delivers a pitch at Citizens Bank Park. (Hunter Martin/Getty Images)

This Washington Nationals season has dwindled enough that you can almost see the next one coming. On Tuesday, because of two pitching performances, you barely had to squint. The Nationals, more than victories even, want promise from young players, and Tommy Milone and Ross Detwiler provided loads of it. That they continued their recent hold over the Philadelphia Phillies only made it sweeter.

The Nationals swept a doubleheader at Citizens Bank Park against the National League East champions, winning 4-3 on Ryan Zimmerman’s 10th-inning, pinch-hit single during the day and 3-0 as the Nationals, led by Danny Espinosa’s home run, battered 11 hits off Cliff Lee at night. The sweep gave the Nationals seven wins in their past nine against Philadelphia and evened the season series at eight games apiece.

More than success against their division bully, the Nationals’ starting pitching performances, from left-handers aged 24 and 25, defined the day. Milone allowed four hits and no walks in six scoreless innings in the first game. Detwiler trumped him at night, facing three batters over the minimum in 7 1 / 3 scoreless innings.

Even against a team that has already clinched the best record in the league, Tuesday felt something like a landmark day. Drew Storen, their 24-year-old closer, ran his season save total to 40 by sealing both wins. Espinosa, their 24-year-old second baseman, ripped three hits, including his 20th home run, off Lee. Espinosa tied a franchise rookie home run record and became the third rookie second baseman to hit 20 homers.

“This,” Manager Davey Johnson said, “is our future.”

Detwiler, the sixth overall choice in the 2007 draft, gave the best performance of his young career. He allowed three singles and a walk and hit one batter while inducing two double plays and striking out three. Detwiler used only 81 pitches for the longest outing of his 27 career starts. He had never recorded an out past the seventh before Tuesday night, and only twice had he recorded an out past the sixth. Detwiler also chipped in an RBI single.

After Detwiler allowed six runs in three innings against the New York Mets on Sept. 2, he studied the tape from that game and decided he needed to focus on throwing his sinker and change-up low in the strike zone. In his two starts since, a span of 13 innings, Detwiler has allowed two runs. Detwiler may be tapping his full potential.

“I just think I have a better mentality going out there,” Detwiler said. “Not necessarily just going to pitch, but going to win, and having more confidence.”

The results mattered little for either the Phillies, who had already clinched the best record in the NL, or the Nationals, who are vying for third place in the division. Washington, though, wanted to find out what it has in young players like Milone, and, albeit against a lineup with three regular starters, Milone showed why he may contend for a spot in the 2011 rotation.

“It puts him in the competition for starting on this ballclub,” Johnson said. “That’s what we want it to do. We need more pitchers like him if we’re going to compete against Atlanta and Philadelphia. I haven’t seen anything that would put him out of the mix yet. He’s been outstanding.”

The Phillies and Nationals both started lineups akin to their junior varsity for the first game. Milone, with three major league starts under his belt before Tuesday, still impressed. Two of his four hits allowed stayed in the infield. Only one runner advanced past second base, and after the Phillies put men on first and third with one out in the sixth of a scoreless game, Milone induced a pop fly and struck out Erik Kratz at a change-up.

“I’d have to say everything” was working, Milone said. “It was actually pretty easy. It didn’t seem like I had to try too hard.”

Milone walked no batters, hit one and struck out two. He befuddled the Phillies with well-spotted fastballs, a devious change-up and a keep-them-honest curveball. None of Milone’s 93 pitches traveled more than 89 mph, but only five of the 24 batters he faced hit the ball out of the infield.

“I’m just trying to make it a little harder on them to decide for next year if I should be here or not,” Milone said.

None of Milone’s pitches, by themselves, overpower hitters. In tandem, and with his precise location and ability to throw cutters and change-ups to all four quadrants of the plate, they make Milone dominant. He struck out 155 and walked 16 at Class AAA Syracuse this season, the best strikeout-to-walk rate at any minor league level.

“He’s good, man,” Zimmerman said. “He throws strikes. He gets on the mound. He goes after people. He knows how to pitch. He doesn’t make mistakes in the middle part of the plate. He knows how to use his stuff to make it overpowering.”

Said veteran starter Livan Hernandez: “He’s very smart. I can see that. He’s got a chance to be good.”

The Nationals still needed extra innings to win the first game. With two outs in the 10th, and Jesus Flores on deck, the Phillies were compelled to intentionally walk Espinosa. Meaningless September baseball can make for fun managing. Johnson called on Zimmerman, who flared an RBI single to center.

“That guy,” said Roger Bernadina, who hit a three-run homer for Washington in the seventh inning, “is clutch.”

After Storen earned his 39th and 40th saves, the Nationals had stretched their road winning streak to six, the longest since baseball returned to Washington in 2005. The Phillies have clinched the best record in the league and the Nationals are vying for third, but against one another they have played to a draw.

“Win or lose, I know we always play them well,” Espinosa said. “And the Phillies know that, too. The Phillies know that we’re not going to come and be a pushover. We enjoy playing here and trying to get some games.”

Tuesday may have been the most promising day of the Nationals’ season. It started with Milone, playing in front of the biggest crowd of his life.

“Especially to pitch in front of a lot fans like that, it’s definitely fun,” Milone said. “I look forward to coming back next year. Hopefully.”