Dahlstrom was cleared to play a day after being struck by a line drive on the outside of his right knee in a 9-7 loss to Westport, Conn., on Sunday.
"Last night, I tried to walk on it, and I was feeling pretty bad," Dahlstrom said following the game. "I tried to walk this morning on it, and I was feeling pretty good."
Washington manager Rob Chandler's expectations regarding Dahlstrom's injury improved, on their way to have the knee examined earlier in the day.
"I saw him on crutches, and I said, 'Maybe we should walk down the hill,'" Chandler said. "We walked down and he was fine."
Dahlstrom drove in Sammamish's second run in the first inning. He added an RBI single in a two-run sixth to build the lead to 6-2.
Sammamish needed the insurance.
With two out in the Iowa's final at-bat, Brook Heinen hit a two-run double to the wall in center, and then scored on a wild pitch. Reliever Will Armbruester, however, ended the game by striking out Grant Garwood.
Iowa (1-2) lost for the first time in 10 games in which it has faced elimination this season.
Brady Roberts had two singles and scored once for the Midwest champions.
Washington's Dylan Matsuoka had two-run single in the third inning.