PHILADELPHIA -- By wrapping up both the National League Wild Card Series and the NL Division Series early, the Phillies have navigated their way to the NL Championship Series while needing to deploy only their top three starters: Zack Wheeler, Aaron Nola and Ranger Su¨¢rez.

That, however, will not be the case in the NLCS.

For the first time this postseason, the Phils will need to call on a fourth starter, though that won't happen until Game 4 on Friday at Chase Field.

By that point, it will have been 20 days since either Taijuan Walker or Cristopher Sánchez?last pitched in a game. Walker's last start came in Game 1 of a Sept. 30 doubleheader against the Mets. S¨¢nchez, who pitched one inning of relief in Game 2 later that night, has not started a game since Sept. 24.

• D-backs-Phillies position-by-position breakdown

While manager Rob Thomson doesn't plan to name a Game 4 starter until after Game 3 on Thursday, both Walker and S¨¢nchez threw two innings in a sim game on Sunday afternoon at Citizens Bank Park.

"I think we have two really good options," Thomson said. "They both threw BP today. Both were a little bit rusty, but that's why we do it."

Walker, who signed a four-year, $72 million deal last offseason, went 15-6 with a 4.38 ERA in 31 regular-season starts. The Phils went 21-10 in those games. S¨¢nchez finished 3-5 with a 3.48 ERA in his 18 starts (he also made one relief appearance). The club went 8-10 in his starts.

"It's all about how we use the bullpen in the next couple of days and also in Game 3," Thomson said.

So while we await the decision, let's take a closer look at how Philadelphia's two options stack up in some key areas.

Matchup vs. D-backs
The Phillies will open the series with a pair of righties in Wheeler and Nola before turning to the left-handed Su¨¢rez in Game 3. Then, they will have an option between the right-handed Walker or the left-handed S¨¢nchez.

The D-backs fared slightly better vs. right-handed pitchers this season. They had a .737 OPS (14th in MLB) and a .414 slugging percentage (15th) vs. righties. Against southpaws, Arizona posted a .711 OPS (21st in MLB) and a .394 slugging percentage (26th).

As for the top threat in the D-backs' lineup, the left-handed-hitting Corbin Carroll did most of his damage this season against right-handers. Arizona¡¯s rookie sensation had a .921 OPS vs. righties compared to just .721 vs. lefties.

That said, the switch-hitting Ketel Marte¡¯s career OPS is 111 points higher against lefties (.874 compared to .763 against righties). As for the club¡¯s two right-handers near the top of the order, Tommy Pham fares slightly better against lefties (.834 compared to .768), while Christian Walker has relatively even splits (.803 and .787).

While Walker also has similar platoon splits against left-handed (.714 OPS) and right-handed (.701) hitters, S¨¢nchez has held lefties to a .557 OPS in his career compared to a .771 mark against righties.

Starting vs. relieving
Given the aforementioned splits, another possibility would be using S¨¢nchez to handle the first inning -- and Carroll's first plate appearance -- as an opener before handing it over to Walker. That would also avoid Walker¡¯s biggest obstacle this season: he had a 7.04 ERA in the first inning (compared to a 3.80 ERA the rest of the game).

That said, Walker has made only three true relief appearances in his career -- and all of them came in 2014. S¨¢nchez, meanwhile, pitched primarily out of the bullpen the past two seasons with the Phillies.

Thus, it's more likely that S¨¢nchez would be used in relief in one of the first three games in the event of an abbreviated start or a lengthy extra-inning game. He'd also be better suited to follow Walker -- as opposed to the other way around -- if Thomson was to use a piggyback approach in which he just asks for two or three innings from each guy.

'Recent' form
Keeping in mind it will have been nearly three weeks since they last pitched, both Walker and S¨¢nchez had some hiccups down the stretch.

Walker had a 5.93 ERA in five September starts. He had just 19 strikeouts while walking 12 over 30 1/3 innings in those outings.

As for S¨¢nchez, he posted a 4.15 ERA over 52 innings in August and September after putting up a 2.30 ERA over 43 innings in eight starts in June and July.

Postseason experience
Neither player has much of a track record when it comes to pitching in the postseason, though

Walker does have one career start under his belt. He took the mound in Game 1 of the 2017 NLDS -- for the D-backs, strangely enough -- against the Dodgers. He lasted only one inning, giving up four runs off four hits and two walks while striking out three.

S¨¢nchez, who was not on the active roster for any of the Phillies' postseason run last year, has never made an appearance in a playoff game.