The first thing you should know about the Seattle rotation is that going into Thursday's action they'd thrown 240.2 innings of 3.93 ERA baseball. That's a tad below the league average ERA for starting pitchers. The second thing you should is that of those 240.2 innings, 47.1 came from Joe Saunders (5.51 ERA), 34.2 from Brandon Maurer (5.97 ERA), 24.2 from Aaron Harang (7.30 ERA), and 10.2 from Blake Beavan (8.44 ERA).

Assuming that you're already aware of whom Felix Hernandez is, then the third thing you should know is the name Hisashi Iwakuma, because he's the only other guy keeping the Mariners rotation in something vaguely resembling working order as the Seattle franchise stumbles through the motions in this young season.

Iwakuma's budding career in Major League Baseball has been easy to overlook until now. Before his hot start to the 2013 season, he was best known for being the guy who Oakland failed to sign after winning his posting rights in the 2011 offseason, causing the posting fee of $19.1 million to be returned to the Athletics and the then 30-year-old righthander to return to Japan for another season with Rakuten. He only pitched 119 innings in 2011, and when the Mariners signed him in the 2011-12 offseason, Iwakuma originally made the club as a reliever out of the pen.

Of course reality got in the way of that, with starters Hector Noesi and Blake Beavan (there he is again) proving unreliable enough that Iwakuma found his way into the rotation. This was the same pitcher who, while healthy for the first few months of the Mariners' 2012, was only able to pitch in five games between the start of the season and June 2, invariably throwing long relief, before manager Eric Wedge decided to start using him like an actual part of the pitching staff and gave him nine appearances in June alone. Iwakuma joined the rotation a month later on July 2 and never looked back, throwing 95 innings of 2.65 ERA ball through the end of the year.

That's a nifty performance, though one that's risky to reward with a fat extension: even including his relief innings from 2012, he only threw 125 IP and was new to MLB, without much tape of him facing major-league quality hitters. But Iwakuma didn't go fishing for a big extension. Without the gaudy numbers to justify a long-term contract from a contending team, he was willing to re-sign with the Mariners on a two-year, $14 million deal, easily within Seattle's budget.

That brings us to the present day, where that deal is working out quite well for the Mariners in a season where very little else is. So far, the key to Iwakuma's success has been excellent command during his starts. He's only walking 1.2 batters per nine innings this year, something not many starters sustain over the course of the season: There's been only 17 pitcher years since 2008 with over 150 innings thrown and a BB/9 less than 1.5, and a number of them belong to guys named Roy Halladay or Cliff Lee (and one belongs to Blake Beavan in 2012, showing that a low walk rate isn't a sure-fire sign of a great pitcher if the reason for it is that the opposition is knocking him all over the diamond). Unlike Beavan last year, however, Iwakuma is also missing bats and striking a lot of guys out, with 55 punch-outs against eight free passes.

It's actually something of a minor miracle that guys are only hitting .209 on balls in play off of Iwakuma, considering the walking-wounded sort of defense that Seattle runs out there every day, and with that comes further skepticism that he can keep stranding nine out of every 10 guys he does let on base -- especially since he's inducing more flyball and fewer groundouts this year than he did last year. But when the corrections come, as they inevitably will, they shouldn't be so vast that they change the dynamics of Seattle's rotation from being Felix, then Iwakuma, and then a bunch of question marks, kids, and journeymen role-players.

A nifty deal indeed, that two-year, $14 million deal for the production he's shown so far -- so nifty that should he keep something resembling this performance up, the Mariners' front office could be fielding a lot of calls about him come the trade deadline. If that's the case, Seattle should be unsentimental and sell high. It's always a good feeling for a team when they strike on a guy no one else valued highly (except presumably Oakland, but they failed to offer him a contract to both parties' liking), but there's danger in overcommitting to those guys. Pay them enough money to prove themselves, then when they've done that, and the market adjusts to value their talents, move on to the next guy.

Sadly for Mariners fans, it's extremely unlikely that Hisashi Iwakuma will be part of the next great Seattle ball club; in fact, it's possible he won't still be pitching in the majors by the time that comes around. The Mariners should enjoy him for now, but it would be wise to prepare for the day -- and it will be someday soon -- when Iwakuma's unexpected success on the mound is worth more to the Mariners with someone else's city across the front of his jersey.