Last season left a bitter taste with the Washington Nationals: World Series favorites heading into the season, the team never got going and was frustratingly mediocre all season until an 18-9 September -- thank you, Mets and Marlins -- pushed their final record to 86-76.

Matt Williams has replaced Davey Johnson as manager, but the toughest question that general manager Mike Rizzo must solve: How to improve this club?

For some teams, the holes are obvious; the Nationals' problems aren't so easy to fix. On paper, it's a team without any outstanding strengths or weaknesses. They finished sixth in the National League in runs scored and sixth in runs allowed. They ranked sixth in rotation ERA and 11th in bullpen ERA, so maybe you can argue they need to improve the relief corps. The bench was horrible in 2013, so that could use an upgrade, but bullpens and benches are notoriously fickle.

While Rizzo will look to improve those areas (although with Rafael Soriano, Tyler Clippard, Craig Stammen and Drew Storen in the pen, you're looking at a second-tier type of reliever), he needs to aim higher.

That leaves two moves Rizzo could do to make the Nationals better.

1. All eight of his starting position players are under contract, but there is one big signing he could make to improve the lineup: Sign Robinson Cano to play second, move Anthony Rendon back to his natural position of third base, and slide Ryan Zimmerman over to first base, where his throwing problems would no longer be an issue. That leaves Adam LaRoche without a job, but you could keep him around for bench strength or trade him to a team that needs a first baseman, like the Pirates.

Financially, signing Cano is feasible. The only players signed long term are Zimmerman (through 2019), Jayson Werth (through 2017), and Gio Gonzalez (through 2016). Of course, at some point the Nationals will need to pony up big money if they hope to keep Bryce Harper and Stephen Strasburg, and right now Cano's asking price is absurdly high.

The other move is more fiscally responsible.

2. While Cano would look nice in the middle of the lineup, the Nationals can expect to score more runs merely from improvement from Harper, a full season from Rendon and better production from the bench. So that leaves the starting rotation. Once you get past Strasburg, Gonzalez and Jordan Zimmermann, it thins out. Ross Detwiler wasn't good last season and battled injuries, Dan Haren is a free agent, and none of the young guys who pitched down the stretch is an elite prospect (Nate Karns is the best one, although Tanner Roark pitched well late in the season).

There are no No. 1 or No. 2 starters in free agency this year (not including Japanese right-hander Masahiro Tanaka), but Ubaldo Jimenez is a guy with No. 1 or 2 potential, and flashed that ability the final four months of 2013 with Cleveland, when he went 10-6 with a 2.40 ERA in 22 starts. He was even more dominant in his final 12 starts, posting a 1.72 ERA. There was nothing that screams fluke in these numbers, as his BABIP was well over .300. Jimenez simply threw more strikes than he has in years and let his natural movement take over.

Yes, he's a risk to fall back into the mechanical nightmares of recent seasons, which led to his struggles in 2011 and 2012 and the first part of 2013, but free agency is the ultimate high-stakes poker game anyway, and it's not like Matt Garza and Ervin Santana don't come with associated risks as well.

Jimenez is the one who can provide the most upside and probably comes in a little less expensive. Plus he has a rubber arm, having made more than 30 starts six seasons in a row, one of just 13 starters to have done that. Garza has battled some injuries, and Santana has been inconsistent and homer-prone despite playing in pitcher-friendly parks.

Plus, Jimenez wouldn't be expected to be the savior in this rotation; he'd merely line up as the fourth guy behind a very good top three. That leaves the Nationals plenty of depth with Karns, Detwiler and Roark battling for the fifth slot. Strasburg, Zimmerman, Gonzalez and Jimenez?

Sounds like a playoff rotation to me.