WASHINGTON - Bryce Harper will have to wait at least one more day to break out of his frustrating slump after Tuesday night's game between the Washington Nationals and Baltimore Orioles was postponed by rain.

The game was called following a delay of approximately 2 hours, 30 minutes. The interleague matchup between crosstown rivals will be made up on Aug. 4.

The teams will continue the home-and-home series in Baltimore on Wednesday night.

Harper came into the game mired in a 4-for-24 skid since his return from the disabled list on June 30. He had left thumb surgery and missed 57 games.

Although the 21-year-old was 1 for 13 over his previous four games, manager Matt Williams was confident the outfielder was on the brink of breaking loose.

"Looks better. Timing's a little better," Williams said Tuesday afternoon. "It's a process man. Take that much time off, it's difficult to maintain timing. So I think he's starting to see it a little bit better, he's a little calmer at the plate. Yeah, the results weren't there, but standing in the dugout watching it, he just looks calmer. It looks like he's seeing the ball a little bit better."

In spite of Harper's struggles, the Nationals started the day a half-game behind Atlanta in the NL East. For that reason, Harper could afford to be patient while waiting for a return to the form that enabled him to win NL Rookie of the Year honours in 2012.

"He knows ... it's going to take some time. Standing in the box he can also feel it," Williams said. "When he's starting to see the ball better he can feel that, too. So it's a question of continuing to work and continuing to go out and play in game situations and see the breaking ball again and again. He'll be good, but it does take time. I'll be happy to write his name in the lineup every day."

The rainout forced the Nationals to shuffle their rotation. Doug Fister, who was slated to start Tuesday, was shoved back to Wednesday. Gio Gonzalez will start Thursday, and Tanner Roark, who was slated to start Wednesday, was moved to the bullpen. Williams said Roark should start Sunday, the final day before the All-Star break.

The Orioles came into the game having won seven of eight. They activated right-hander Bud Norris from the disabled list to make his first start since June 21. He had been sidelined with a strained groin.

Norris will start Wednesday instead, and Wednesday's scheduled starter, Wei-Yin Chen, was pushed back to Thursday.

Williams said talk of a day-night doubleheader Wednesday in Washington, then Baltimore, was never discussed.

"Didn't the Mets and Yankees do it at one point?" the manager asked. "I would imagine that it was about the same amount of time to get across New York City that would take for us to get to Baltimore, but no, we had a mutual off day on the 4th of August so we'll determine what time that game is. Since there was a mutual off day we didn't go that far."