WASHINGTON -- At the start of the season, the top four starting pitchers for the Washington Nationals were clear: Max Scherzer, Stephen Strasburg, Tanner Roark and Gio Gonzalez.

Scherzer and Strasburg were selected to the National League All-Star team on Sunday, and Gonzalez is having one of his best seasons in years.

However, with the struggles of Roark, who has a 5.27 ERA after winning 16 games last year, Joe Ross could be an important figure in the coming weeks for the first-place Nationals.

Ross (4-3, 5.12 ERA), who began the year at Triple-A Syracuse, will take the mound on Tuesday against the New York Mets. The game at Nationals Park will start at 11:05 a.m. EDT to accommodate fans who want to see the fireworks on the National Mall on Tuesday night.

"I have never had any major league games at that time," said Mets manager Terry Collins, who managed minor league games in the morning. "It will certainly be different for everybody."

Ross will be opposed by Mets right-hander Seth Lugo (3-1, 3.55 ERA), who is 1-1 with a 2.30 ERA in three games against Washington in his career.

The series is obviously important for the Mets, who trail the Nationals by 10 1/2 games after Washington won 3-2 Monday with a walk-off single in the ninth by Ryan Raburn.

"They are all aware," Collins said. "They know these are important."

Mets left fielder Yoenis Cespedes came up limping when he almost caught the hit by Raburn in the ninth Monday. Collins said with an early start Tuesday, it is unlikely the slugger will be in the starting lineup.

"It's just a cramp. It could have happened to anybody," Cespedes said through a translator.

Ross also may not have to deal with outfielder Curtis Granderson (hip), who was out of the starting lineup Monday but slugged a pinch-hit homer in the ninth to tie the game at 2.

In Ross' last start, at home Thursday against the Chicago Cubs, he gave up five hits and just two runs in 6 2/3 innings. He was in line for the win before the bullpen allowed three runs in the ninth in a 5-4 loss.

Ross is 1-2 with a 4.71 ERA in five career starts against the Mets. Current Mets hitters are batting 31-for-94 (.330) against him with five home runs.

Lugo last faced the Nationals on June 17 in New York, when the Mets lost 7-4 as he went 6 2/3 innings and gave up four runs, three earned.

He earned the win in New York against Washington on Sept. 4, 2016, when he went seven innings and gave up one earned run on six hits with no walks and four strikeouts.

The Mets pitcher most likely will have to face Daniel Murphy, the former New York second baseman who got the night off Monday before he was retired as a pinch hitter in the eighth.

"We have to keep Murphy healthy," Washington manager Dusty Baker said Monday. "He will be back in there tomorrow. Forty-six games in 48 days -- that is a lot of baseball. I am just trying to keep guys strong."

Murphy, first baseman Ryan Zimmerman and outfielder Bryce Harper were all the top National League All-Star vote-getters at their positions and will be starters in the All-Star Game on July 11 in Miami.

"It is a blast," Harper said Monday. "You are among the best of the best. It is a huge honor. It's definitely humbling and a blessing."

Baker doesn't have a problem with so many of his players taking part in the Mid-Summer Classic.

"I always want them to get the accolades they deserve," the manager said. "They definitely deserve to go to the All-Star Game."