Employing a wood-breaking two-seam fastball, the Astros prospect pitched six more shutout innings -- running his scoreless streak to 14 1/3 -- as the Tri-City ValleyCats beat the Aberdeen IronBirds, 5-1, on Sunday.
Dufek (2-0), an 11th-round pick in last month's draft, allowed four hits and struck out three. He induced 11 groundouts.
"I never really used it in college, and these last two outings I have been working my two-seamer down and in to righties and down and away to lefties," said Dufek, who oddly had just one 1-2-3 inning. "It's been getting ground balls for me and working well."
Opposing Vermont on July 4, the former Creighton University standout scattered six hits over six shutout innings. The scoreless streak goes back to a start on June 29 -- a day before his 23rd birthday -- when he yielded two runs over six frames at Lowell.
Dufek began incorporating a counterbalance to his four-seam heater shortly after giving up seven runs -- six earned -- on eight hits over 3 2/3 innings against Lowell in his second pro outing on June 24.
"It just happened to be after a tough outing," he said. "We were throwing in the bullpen and I was throwing a two-seam, and [pitching coach Gary] Ruby and I were talking while it was moving. And we were like, 'We're going to keep working on that pitch.'"
After almost three weeks of development, Dufek said he will throw the two-seamer inside to righties and outside to lefties while he continues to use his four-seamer outside to righties and inside to lefties.
Five starts and 24 2/3 innings into his pro career, he's 2-0 with a 2.92 ERA.
"It's a different game and a different experience," Dufek said, "but I have really enjoyed it so far. I loved my time at Creighton, but I love what I am doing here so far. And I'm just living the dream right now."
Another member of the Astros' 2011 draft class, 15th-rounder Zachary Johnson, fell a triple shy of the cycle and plated two runs. Just 2-for-19 entering Sunday, he slugged his first homer in 22 games.
"I know he hasn't been hitting the ball the way he would like to lately, but today he busted out," Dufek said, "It really helps a pitcher when you have guys like that."