They're headed for a possible collision in the National League Division Series presented by T-Mobile, provided they can heal quickly from identical injuries -- supposedly mild strains in the right hamstring.
The Cubs-Nationals matchup never lacked for intrigue, but the handling of Scherzer and Arrieta adds a little bit of mystery to a series that will probably need all five games to determine who moves on to the NL Championship Series.
Fortunately, both starting rotations are about as thick as any this side of Cleveland, so neither team should feel like its hopes are tied up in what happens in bullpen sessions or the privacy of the trainer's room. But everyone involved is watching closely to see if Scherzer's "tweaked'' hamstring is less serious than Arrieta's Grade 1 strain.
We'll find out soon enough. Both are expected to throw bullpen sessions on Wednesday.
While Nationals manager Dusty Baker hasn't said who will start Game 1 tonight, it seems significant that Stephen Strasburg threw a full bullpen during a Tuesday workout while Scherzer only played catch off flat ground. Consider Strasburg a strong 1A.
"He's pretty good,'' Cubs manager Joe Maddon said at a Wrigley Field workout on Tuesday.
No kidding. Strasburg (15-4, 2.52 ERA with 204 strikeouts in 175 1/3 innings) was the NL Pitcher of the Month in September. He has become the force he was projected to be eight years ago, when the Nationals took him first overall in the 2009 Draft, strongly believing they could land Bryce Harper first overall the next year.
This was the 1-2 punch that was projected to make the Nats a perennial contender for the World Series, but they've yet to get past the NLDS. In Scherzer, Strasburg, Gio Gonzalez and Tanner Roark, they believe they have a rotation built for a long ride this time around.
The Nationals (3.63) and the Cubs (4.05) ranked third and fourth in the NL in rotation ERA this season. But they were 1-2 in the league in the second half of the season, with the Cubs at 3.36 and the Nationals at 3.53. Only the Indians' rotation was better.
Jon Lester, one of the tougher October pitchers all time, and 2016 NL ERA champ Kyle Hendricks give the Cubs strong options alongside Arrieta. Jose Quintana, acquired from the White Sox in July, is another solid choice for the Cubs. They have John Lackey and lefty Mike Montgomery in the wings if they need them, which gives president of baseball operations Theo Epstein and Maddon a feeling of security.
But the Cubs are at their best when Arrieta is at his best. That's the way it has been for three seasons under Maddon, and they'd love to get one more strong October out of him before he hits free agency.
Arrieta has had a big second half (6-3, 2.28 ERA in 12 starts) but twice left starts early because of pain in the leg he uses to push off the mound -- first on Sept. 4 in Pittsburgh and again last Tuesday against the Cardinals. He's spent a lot of the last week getting a variety of treatments on his leg (including the use of a hyperbaric chamber) and will throw a bullpen Wednesday that he expects to be uneventful.
Arrieta insists he isn't worried about how he'll hold up.
"Not really,'' he said. "I'm strong enough where I can take a little bit of effort off from my lower body, really focus on just finishing with my upper body, get out there with extension. I'm rarely trying to throw the ball physically as hard as I possibly can. There is some wiggle room in there to control the effort, if that's what I have to go through and deal with for the remainder of the season, I'm capable of doing that.''
Maddon said Tuesday he is confident Arrieta will be in the rotation, but hasn't hinted where he might fall. Smart money seems to be that Lester and Hendricks will get Games 1 and 2 in Washington, but depending on the outcome of Wednesday's session, Arrieta could put himself in that equation as well.
Scherzer is in the same boat. He told reporters on Tuesday that he expects to be in the NLDS rotation, but doesn't know where he'll slot in.
It would be fitting if Arrieta and Scherzer wound up facing each other.
Both teased their teams for years before having breakout performances in their age-28 seasons. Scherzer won the first of his two Cy Young Awards for the Tigers in 2013, going 21-3 with a 2.90 ERA. Arrieta turned the corner for the Cubs in the second half of '14, flashing the fastball command and filthy slider he'd use to put together a historic second half and win the Cy Young in '15.
When Arrieta was emerging as a force, it made Maddon think of the young Scherzer.
"He had this video-game stuff," Maddon said of Scherzer in his early days with the D-backs and Tigers. "It was just so good, and then he finally figured it out, and now he is who he is. There's a similarity there [with Arrieta] in regards to figuring out where his fastball is going and being able to play off it, because his other stuff is outstanding, also. If your fastball isn't good, the other stuff isn't quite as good, either."
Scherzer declined a chance to stay with the Tigers and was rewarded with a seven-year, $210 million deal from the Nationals. Arrieta has been open about his desire for a seven-year contract, and it appears the Cubs are prepared to allow him to chase his next deal on the open market. But he's got at least one more chapter to write in Chicago. Scherzer and the Nationals have some unfinished business of their own.
Here's wishing good health for both of them. It would be a shame to see this showdown diminished.
Phil Rogers is a columnist for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.