It’s usually one of the better non-scientific indicators of how many Orioles fans are in a road ballpark. And during Sunday’s national anthem before the Orioles series finale in Washington, the “O” was head-shakingly loud.

You could look into the seating bowl of Nationals Park and see nearly as much orange as you could red -- that is up until the eighth inning of the Orioles' 9-3 loss. Most of them were seen filing toward the exits then.

This weekend’s Battle of the Beltway series lived up to its hype in a lot of ways. The Orioles took two tightly contested games here before the Nationals avoided a sweep with Sunday’s win.

And the Orioles fans filled Nationals Park in droves. The Saturday and Sunday games were the Nationals’ first back-to-back crowds of more than 40,000 fans, and the series’ three-day total of 120,929 (an average of 40,309) surpassed the top three-day total at Camden Yards this season (the home opener series vs. Minnesota) by nearly 27,000 fans.

It helped that for the first time both teams are suddenly contenders, but it was surreal to see Orioles fans “take over” a road park much like Camden Yards is regularly filled by boisterous fans of the Yankees and Red Sox.

“I know they’re excited about having so many of our fans here,” Orioles manager Buck Showalter said of his team. “We had some last year. It was a pretty good turnout last year, but it’s kind of like at our ballpark with the Red Sox fans and the Yankee fans. I think it’s just good for baseball to have that many people come here and watch a game. I know it’s not free and they have a lot of decisions to make about what to do that night or that afternoon. For them to want to watch what we’re doing is an honor.”

And now, the Red Sox come to town.