Washington’s Jordan Zimmermann, who posted a 2.66 ERA, heads up a starting rotation that led the majors with a 3.04 ERA, ranked second with a 4.05 strikeout-to-walk rate and finished fifth with 1,0021 / 3 innings pitched. (Patrick Smith/Getty Images)

Each day, we’ll be taking stock of every Washington Nationals positional group. Part 1 of 5: The starting rotation.

Season review

The Nationals returned their stellar core of Stephen Strasburg, Jordan Zimmermann and Gio Gonzalez, and they found two stalwarts in sudden star Tanner Roark and trade acquisition Doug Fister.

The result gave the Nationals perhaps the best starting pitching in the major leagues. They led the majors with a 3.04 ERA, ranked second with a 4.05 strikeout-to-walk rate and 17.6 wins above replacement and finished fifth with 1,0021 / 3 innings pitched. The 2014 Nationals were strong across the board, but their strongest piece was their rotation.

Strasburg surpassed 200 innings for the first time in his career, producing one of the best extended stretches of his career at the end of the regular season before making a lukewarm playoff start. Zimmermann made his second all-star team, punched up a career-best 2.66 ERA and struck out 8.2 hitters per nine innings, an increase of 1.4 over 2013. He solidified himself as one of the best right-handed starters in baseball.

Roark emerged as a reliable, often excellent back-of-the-rotation starter who posted a 2.85 ERA over 1982 / 3 innings and, best of all for the Nationals, will make the league minimum for another two years. Fister was an absolute steal from the Tigers, going 16-6 with a team-best 2.41 ERA after missing the season’s first month with a lat strain. He also dominated in the Nationals’ only postseason victory. Gonzalez landed on the disabled list for the first time in his career after struggling through shoulder tightness, but by the end of the season had returned to form — and then fumbled away NLDS Game 4 with two costly defensive miscues.

Offseason outlook

The biggest decision facing the Nationals is whether they can sign Zimmermann and/or Fister to contract extensions that will take them beyond the 2015 season, when both will be eligible for free agency.

The Nationals engaged with both about long-term extensions last season. They reached a two-year, $24 million deal with Zimmermann, $16.5 million of which he’ll make in 2015. They shared dialogue about a longer deal, but the talks stalled. The Reds did the Nationals no favors when they signed Homer Bailey to a five-year, $105 million extension. Given that deal and Zimmermann’s excellence this season, any contract Zimmermann signs will likely be the largest the Nationals have ever given.

Fister, who owns a career 3.34 ERA in nearly 1,000 innings, would not command the same nose-bleed salary as Zimmermann, but an extension for him would look similar to Bailey’s, if not surpass it.

If the Nationals cannot come to a long-term agreement with either, they at least would have to consider trading one or both, lest they risk watching a valuable asset sign elsewhere in a year with only a compensatory draft choice in return.

Roark is a low-cost lock to return. Gonzalez’s deal, a sweetheart contract for the Nationals, calls for him to make $11 million in 2015. Strasburg will receive a nice bump from the $3.98 million he made last year through arbitration, but he remains affordable, especially in relation to his ability and production.

Possible free agent targets

In the likeliest outcome, the Nationals will not need to shop for free agents. In the less likely event the Nationals trade Zimmermann or Fister, veterans Jake Peavy, Jason Hammel and Ryan Vogelsong may make sense as cheaper, short-term options. Given the depth they’ve built, though, the Nationals are unlikely to add starting pitching via the free agent market.

Prospect to watch

Right-hander A.J. Cole, who turns 23 in January, could slide into the top 50 of major prospect lists this spring after he went 13-3 with a 3.16 ERA over 134 innings between Class AA and Class AAA this season. Cole struck out 50 and walked 17 in 61 innings at Class AAA Syracuse to end the season. The Nationals need to add him to their 40-man roster this winter to protect him from the Rule 5 draft and so he will have a clear path to the majors.

The Nationals drafted Cole in 2010, traded him in December 2011 to the Oakland Athletics and re-acquired him in a three-way trade in January 2013. After a winding path, Cole may be ready to make a big league impact.