"It's just great to see," said Hall of Famer Frank Robinson, who has managed both clubs and was an iconic player for the O's. "It's great for the cities, for the organizations and especially for the fans."
To the people who long dreamed of having Major League Baseball in both cities, to those who worked so hard for so long and thought it was a great idea whose time had come, this season is the fulfillment of years of hard work.
"There are great baseball fans in both cities," Robinson said. "Some people may be surprised about Washington. I'm not. I knew the interest was there. You could tell when you were out and about in the city. People wanted to talk baseball."
There hasn't been a postseason baseball game in the nation's capital since the Senators lost the 1933 World Series to the New York Giants. In Baltimore, it has been 15 years, which is a blink of the eye by comparison.
(Babe Ruth was hired by a Washington newspaper to write a column during that '33 World Series. Unfortunately, he was competing against the Washington Post's Shirley Povich, who was the "Babe Ruth" of sports columnists. Legend has it that Ruth showed up for his first assignment, and then was not seen or heard from again. Even the Bambino didn't want to compete against Povich, who died in 1998 after campaigning tirelessly to bring Major League Baseball back to his hometown after the Senators left for Texas in '72.
For the dozens and dozens of Povich's friends, this season of Washington baseball is a reminder of how much he would have loved it. He received the first and only 75-year pin in the history of the Post. When Cal Ripken Jr. broke Lou Gehrig's "Iron Man" record of 2,130 consecutive games, Povich was the only man in the house who knew both Gehrig and Ripken.)
But I digress.
For years, there was a feeling among Major League Baseball owners that Washington and Baltimore couldn't support two teams. The Orioles worked hard to draw fans from Washington, and they marketed the team as a regional club.
At one point, the O's said they were getting more than a third of their fans from the Washington area. Still, many believed that after years of explosive growth in the Washington suburbs, the area was more than capable of supporting a second team.
Beyond the Major League attendance numbers, five Minor League teams in the area could draw close to 500,000 fans this season.
When the Expos arrived in Washington in 2005, they drew 2.7 million fans that first summer. Attendance declined as the team struggled, but there was little question that the interest was there, that fans were looking for a reason to return.
Now, thanks to an exciting young team and a beautiful ballpark a mile south of the United States Capitol, the Nationals are drawing almost 30,000 fans a game at home.
It did not happen overnight. After relocating from Montreal, the Nats played their first three seasons at old RFK Stadium.
It was an aging, iconic structure whose best days had passed. When the club moved into Nationals Park in 2008, it seemed clear that Washington was about to have something special.
During six straight losing seasons, Nats general manager Mike Rizzo was constructing a great organization. His work is on display this summer with a team that has spent 97 days alone atop the National League East, and Washington has one of the game's most marketable stars in 19-year-old Bryce Harper.
Now, about the Orioles. They're on their way to breaking a string of 14 consecutive losing seasons and having their best attendance season (25,000 per game) since 2007.
Executive vice president of baseball operations Dan Duquette and manager Buck Showalter have done a spectacular job in turning the franchise around. Inside the clubhouse, a core group of very good players -- Adam Jones, Matt Wieters and Jim Johnson, among others -- are having the time of their lives.
The Orioles drew 3 million fans in each of their first eight full seasons at Camden Yards. Attendance declined in recent years, but there was an electric atmosphere this weekend as a four-game Yankees-O's series drew 173,573 fans.
"Baltimore is a proven great baseball city trying to fall back in love with its team," said George Will, a syndicated columnist, ABC News analyst and longtime baseball fan.
The Cubs are No. 1 in Will's heart, but he had season tickets to both the Orioles and Nationals for years.
"They are very different situations," Will said. "Washington has been a football town since the '70s. It's this great, sprawling cosmopolitan area full of people from someplace else."
Washington has fan clubs dedicated to the Tigers, Red Sox, etc., but a new generation of fans is coming of age, and they're buying Bryce Harper and Ryan Zimmerman jerseys and falling in love with the pennant race.
Players on both teams say they're proud of helping turn their franchises around. They're proud, too, when they soak in those games when the place is rocking and loud and electric.
"You have to realize it takes time," said Jones, the O's All-Star center fielder. "When you've lost for 14 years in a row, people are not going to come back overnight. But they're coming back, and they're excited."
Forty miles away, there was a similar feeling.
"It's great for the area," said Nats manager Davey Johnson, who, like Robinson, played for the Orioles and managed both clubs. "It has been a fun summer to be a baseball fan here."