Tanner Roark got an icy surprise as a reward for nine shutout innings against the Angels. (Greg Fiume/Getty Images)

The Nationals brain trust -- Matt Williams, Steve McCatty and Mike Rizzo -- will have a decision about the makeup of their rotation when Doug Fister returns from a lat strain, which could happen as soon as May 7. Tanner Roark is doing all he can to take that decision out of the trio's hands.

Roark befuddled the Padres on Saturday, throwing a complete game shutout in the Nationals' 4-0 win. He allowed just three hits and one walk while striking out eight, a new career high. Roark doesn't have overpowering stuff, but he commanded the zone masterfully against the Padres. They didn't get their first baserunner until the sixth inning, and never got a runner to third base. They put two men in scoring position all game, and one of those was with the help of an error.

It was easily the best start of Roark's career, and it couldn't have come at a more opportune time for his immediate future. Fister threw a 40-pitch bullpen session on Thursday and reported no ill effects. He is scheduled to make his first rehab start on Sunday, and the team is hopeful he will only need two before coming off the DL. If he can stay on that timeline, he'd likely make his Nationals debut in their three game set against the Dodgers from May 5 to 7, or their weekend series in Oakland. That means either Roark or Taylor Jordan will move to the bullpen, and the former appears to have the clubhouse lead for that final rotation spot.

Roark was solid, but not spectacular, in his first three outings of the year, notching two quality starts. He got knocked around a bit by the Braves, but pitched well enough against the Mets and Marlins, allowing five runs and 13 hits in 12 1/3 innings in those two starts. He has been much better his last two times out, though, including Saturday's domination of the Padres. Against the Angels on Monday, he tossed 6 2/3 shutout innings, surrendering seven hits and two walks with five strikeouts. Meanwhile, Taylor Jordan has struggled in the early going, posting a 6.23 ERA, 4.43 FIP and 1.71 WHIP in 21 2/3 innings.