With just over a month left in the regular season, the Nationals have a solid starting rotation with the best ERA in the National League. Assuming the playoffs started tomorrow, the Post Sports Live crew debates which Nationals pitcher should start Game 1. (Post Sports Live/The Washington Post)

Baseball’s schedule is unrelenting. After capping one of the most memorable stretches in team history, the Washington Nationals were swept in Philadelphia by a last-place division foe. But there’s no time for reflection. Now, sandwiched between off-days, the Nationals face perhaps their toughest six-game stretch of the season.

In their final West Coast swing, the Nationals will square off against the surprising Seattle Mariners and the National League West-leading Los Angeles Dodgers. Both are among the best in their respective leagues. With mixed results against winning teams this season, the Nationals have a chance to measure themselves against some of baseball’s elite.

“It’s going to be a big test for us,” Nationals center fielder Denard Span said. “We’ve just got to take one game at a time and just grind out victories, and that’s it really.”

The week, however, isn’t notable simply because of the quality of opponents. The Nationals will face some of baseball’s best pitchers, an early test of the quality of starter they might face in October.

The trip starts Friday night against one of the American League’s top pitchers, veteran right-hander Felix Hernandez, whom the Nationals and starter Jordan Zimmermann have never faced. Chris Young, who spent last season and this spring training with the Nationals, will look to continue his resurgent season (3.17 ERA) on Saturday. Sunday’s starter, Hisashi Iwakuma, finished third in the AL Cy Young voting last season and has a 2.83 ERA this season.

The Post Sports Live crew debates what the odds are that the division-leading Baltimore Orioles and Washington Nationals meet in the World Series. (Post Sports Live/The Washington Post)

Then on Tuesday in Los Angeles, Doug Fister will step into the batter’s box against the best pitcher in the NL, left-hander Clayton Kershaw.

“We have to execute,” Nationals Manager Matt Williams said. “It’s important to execute, especially against pitchers like that because they’re not going to give many opportunities. The measuring stick? We’ve got to play the game, and we’ve got to take advantage of opportunity, and if we execute them, we have a chance, whoever is out there, to beat them.”

Hernandez and Kershaw will be the Nationals’ stiffest tests. Kershaw leads the major leagues with a 1.73 ERA, 1.81 FIP (Fielding Independent Pitching ERA) and 0.84 WHIP (walks and hits allowed per inning) over 1611 / 3 innings, including a no-hitter in June. Hernandez is third in ERA (2.07) and second in FIP (2.22) and WHIP (0.89) over 191 innings. At one point this season, Hernandez set a major league record with 16 straight starts of at least seven innings and no more than two runs allowed.

“He’s just aggressive,” Williams said. “He throws a fastball in there and a good change-up, split change and a slider. He’s a good pitcher. We’re gonna have to do things right to have a chance to beat him. So that takes good pitching on our side, making sure we don’t give them extra outs, taking advantage of guys who get in scoring position. That’s the same with any pitcher. But he’s special. He’s the best pitcher in the American League as far as what I’ve seen this year.”

Kershaw, the NL’s reigning Cy Young Award winner, is 6-2 with a 2.79 ERA against the Nationals over seven seasons. On May 6, in his first start back from the disabled list, Kershaw tossed seven scoreless innings and struck out nine in Washington. The Nationals took the other two games of that series.

“It’s going to be a good measuring stick” for us, Span said. “We’ve got Felix on Friday and Iwakuma on the last day. And in L.A., every given night they’re throwing a No. 1 or No. 2 caliber starters.”

With 30 games left in the regular season, the Nationals hold a six-game lead over the Atlanta Braves in the NL East, so this six-game swing won’t define their season. The Nationals have six games remaining against Atlanta.

But the Nationals sit 18 games over .500 thanks in part to beating up on losing teams. Seattle, however, has a plus-101 run differential, third best in the AL, and Los Angeles boasts a plus-55 run differential, second only to the Nationals in the NL, who also have a plus-101 differential. Run differential is a good indicator of the strength of a team, its pitching staff and offense.

The Nationals are 23-30 against teams with a .500 record or better, the worst mark of all the division leaders in baseball. Against teams with losing records, the Nationals are 52-27, the second-best mark in the majors. Despite that, the Nationals don’t view the Mariners and Dodgers as a chance to prove themselves.

“We don’t think that way,” Williams said. “We never, ever think that way. We know that if we do things correctly, we have a chance to beat the other team on any given night. And that’s how we approach it every single day, regardless if we have a winning streak or we’ve lost three in a row. It doesn’t matter. It’s the same approach.”

Against AL contenders, the Nationals have done poorly, going a combined 2-8 against Baltimore, the Los Angeles Angels and Oakland. All would make the playoffs if the season ended today. Against contending NL teams, the Nationals have done much better, a combined 13-10 against Milwaukee, San Francisco, St. Louis and the Dodgers.

“I don’t think we’re measuring anything,” Nationals shortstop Ian Desmond said. “We know who we are. Just a couple more games. It’s gonna be good for us to get an off-day [Thursday], everyone regroup. Go on to the next series and forget about [the Phillies] one.”