Austin Voth will start Tuesday. (Patrick Semansky/AP)

PHILADELPHIA — The Washington Nationals plan to start right-hander Austin Voth on Tuesday in the series opener in Baltimore against the Orioles, Manager Dave Martinez said Sunday morning.

“That’s as far as we got so far,” Martinez said. “After [Sunday’s] game, I’ll sit down with [General Manager Mike Rizzo] and figure out what we’re going to do.”

The Nationals still need to decide who will start Wednesday in the series finale against the Orioles. The team faces a decision about whether to use a four-man rotation out of the all-star break and throw Stephen Strasburg, its top available pitcher with ace Max Scherzer on the injured list, or stick with a five-man rotation despite Monday’s day off by using another spot starter. If Strasburg pitches against the Orioles, the worst team in baseball at 28-64 entering Sunday, he will not be available for the Nationals’ four-game weekend set against the National League East-leading Atlanta Braves.

The Nationals need to make up ground in Atlanta despite their franchise-best 30-11 stretch in their past 41 games entering Sunday because the Braves were the second-best team in baseball over that span at 28-14 and maintained a six-game division lead.

Voth, 27, shined in his season debut against the Braves on June 23, touching 96 mph with his fastball and giving the Nationals six innings while allowing two runs on four hits and yielding no walks against seven strikeouts. In his next two outings, against two of baseball’s worst offenses in the Detroit Tigers and Kansas City Royals, he lacked the same sharpness. He went 4 1/3 innings in both starts and combined to allow seven runs on 11 hits and five walks.

Voth said he felt “a tick off” after both starts and struggled to locate his fastball to the glove side. Just before the all-star break, the Nationals sent Voth to Class AA Harrisburg, where he allowed two hits over six scoreless innings in his lone start there Thursday. Martinez seemed heartened by the progress — and he hoped it would continue for the Nationals on Tuesday.

Nationals (49-42)

Trea Turner, SS

Adam Eaton, RF

Anthony Rendon, 3B

Juan Soto, LF

Matt Adams, 1B

Brian Dozier, 2B

Kurt Suzuki, C

Victor Robles, CF

Aníbal Sánchez, RHP

Phillies (47-45)

Scott Kingery, 2B

Jean Segura, SS

Bryce Harper, RF

Rhys Hoskins, 1B

J.T. Realmuto, C

Jay Bruce, LF

Maikel Franco, 3B

Adam Haseley, CF

Jake Arrieta, RHP