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8/26/2014 8:54 P.M. ET

Nationals plan to let Roark keep pitching

PHILADELPHIA -- After Monday night's outing, Tanner Roark moved further past his previous high for innings in a single season. In 2013, the right-hander threw 159 1/3 innings between Triple-A Syracuse and the Major League club, but his six-inning effort Monday night gave him 166 2/3 innings with the Nationals this season.

Roark, who has gone at least six innings in 20 of his 26 starts and has pitched seven or more in 12 outings, has a 12-8 record, a 2.81 ERA and a 1.09 WHIP in 2014.

"We are in the business of winning games and we're going to continue to give him the ball and have him pitch for us because he's been really, really good," Nationals manager Matt Williams said. "But we have to keep on eye where he gets to and how many innings he gets to."

Williams said the 27-year-old's workload is being monitored, but he won't be skipped in the rotation at any point.

"Because he's in uncharted territory and he's never been here before, we'll try to, within the game or within his start, try to help him out if we can," Williams said. "But geez, if he's 75 pitches through seven and we're in a tight game, there's no reason just to take him out because he's pitched well to get there. So we want to give him that chance.

"There may be situations like that if we have a lead, a good lead and he's through seven, we may not send him out in the eighth. So that's what I mean. Not necessarily skipping him, but being mindful of where he's at, innings-wise, pitch-count-wise. And if those situations arise, then look at potentially getting him out of a game if we're ahead and if we're comfortable in that regard. In that regard, too, we also have to be mindful of the back of our bullpen, which is important, too."

Severino, Rivero among Nats' AFL-bound prospects

PHILADELPHIA -- The Arizona Fall League announced its preliminary rosters for the 2014 season on Tuesday, and seven players in the Nationals' organization will head west to compete in the six-week league that begins its season on Tuesday, Oct. 7.

"Approximately 60 percent of our players will reach the Major Leagues," AFL director Steve Cobb said. "We want fans to know top young professional talent still will be playing baseball in October and November in Arizona."

Left-handed pitcher Felipe Rivero, the Nats' No. 17 prospect, and catcher Pedro Severino (No. 12) are among the AFL-bound prospects. Rivero has thrown 49 innings and made 13 starts in the Minors this season, compiling a 3.49 ERA and a 42/17 strikeout-to-walk ratio. Severino, meanwhile, has logged 89 games and 274 at-bats with Class A Advanced Potomac in 2014 and has a .248 batting average with eight homers and 31 RBIs.

Other Nats pitching prospects on the AFL team include lefty Matt Grace, righty Neil Holland and righty Derek Self. Second baseman Tony Renda (No. 18) and catcher Spencer Keiboom round out the Nationals' representatives.

Souza named International League MVP, top rookie

PHILADELPHIA -- Before his callup to the big leagues on Aug. 3, outfield prospect Steven Souza Jr. was lighting up the International League with Triple-A Syracuse. On Tuesday, it was announced that his efforts -- which included league leading marks for batting average (.354), on-base percentage (.435) and slugging percentage (.601) -- earned him the league's MVP and Rookie of the Year honors.

Souza, who is the first Chiefs player to win both MVP and Rookie of the Year honors in the same season, also hit 18 homers, drove in 70 runs and swiped 24 bases. The Nationals' No. 5 prospect is currently rehabbing from a shoulder injury at Class A Advanced Potomac, and seems poised to be added back to the Nats' roster when rosters expand on Sept. 1.

The 25-year-old's historical season coincided with Syracuse manager Billy Gardner Jr. earning International League Manager of the Year honors.

"I just think he took a major step forward," Nationals manager Matt Williams said. "Him and certainly Michael Taylor took major steps this year. And that's gratifying to see. It speaks to our player development guys. Certainly the managers, Billy Gardner, who was the Manager of the Year, congratulations to him as well. It just speaks to the way they help these kids get to where they want to get to. So they've both been in the big leagues this year. They're both close to being here on an everyday basis. And we're happy for them. It takes a lot of hard work, and a lot of dedication by a lot of folks to have guys that are named MVPs and Rookies of the Year and things like that."

Worth noting

First baseman Adam LaRoche is dealing with back tightness, and Williams attributed it to how much he's played.

"Adam's dealing with a tight back for three or four days. Today, it's a little worse. It's an opportunity to give him some rest," Williams said. "He just gets tight every once in a while. He plays a lot. He's been on the bases a lot. We've had some long games. All of that contributes to it. But he was in [the lineup] originally until we talked today. He's a little tight.

"He's just gonna chill out today and get some work done, and hopefully, it'll alleviate itself tonight and he'll be good to go tomorrow."

Erik Bacharach is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.